A method for diagnosing schizophrenia, schizo-affective disorder and/or psychosis in an individual or predicting risk of the individual for developing schizophrenia, schizo-affective disorder or psychosis, the method comprising: (i) determining values for one or more markers in each of five domains in one or more biological samples obtained from the individual: (a) a neurotransmitter domain comprising dopamine, noradrenaline and adrenaline; (b) an oxidative stress domain comprising urinary hydroxyhemopyrroline-2-one and urinary creatinine, and/or other marker of oxidative stress; (c) a nutrition-biochemistry domain comprising free copper to zinc ratio, activated vitamin B6, red cell folate, serum vitamin B12, and vitamin D; (d) a visual processing domain comprising visual span, visual speed of processing discrepancy, visual speed of processing, and distance vision on right; and (e) an auditory processing domain comprising reverse digit span, competing words discrepancy, auditory speed of processing discrepancy, and auditory speed of processing; and (ii) comparing values for said one or more markers in each of said domains to control values of said markers in subjects not suffering from schizophrenia, schizo-affective disorder or psychosis, wherein the values of said markers indicative of schizophrenia or psychosis are, relative to said control values: - in the neurotransmitter domain, high dopamine, high noradrenaline, and high adrenaline; - in the oxidative stress domain, high urinary hydroxyhemopyrroline-2-one divided by urinary creatinine; - in the nutrition-biochemistry domain, high free copper to zinc ratio (or low zinc to free copper ratio), low activated vitamin B6, low red cell folate, high serum vitamin B12, and low vitamin D; - in the visual processing domain, low visual span, high visual speed of processing discrepancy (percentage of age), low visual speed of processing (percentile), and poor distance vision on right; and - in the auditory processing domain, low reverse digit span, high competing words discrepancy (percentage of pass score), high auditory speed of processing discrepancy (percentage of age), and low auditory speed of processing (percentile). (i) determining values for one or more markers in each of five domains in one or more biological samples obtained from the individual: (a) a neurotransmitter domain comprising dopamine, noradrenaline and adrenaline; (b) an oxidative stress domain comprising urinary hydroxyhemopyrroline-2-one and urinary creatinine, and/or other marker of oxidative stress; (c) a nutrition-biochemistry domain comprising free copper to zinc ratio, activated vitamin B6, red cell folate, serum vitamin B12, and vitamin D; (d) a visual processing domain comprising visual span, visual speed of processing discrepancy, visual speed of processing, and distance vision on right; and (e) an auditory processing domain comprising reverse digit span, competing words discrepancy, auditory speed of processing discrepancy, and auditory speed of processing; and (a) a neurotransmitter domain comprising dopamine, noradrenaline and adrenaline; (b) an oxidative stress domain comprising urinary hydroxyhemopyrroline-2-one and urinary creatinine, and/or other marker of oxidative stress; (c) a nutrition-biochemistry domain comprising free copper to zinc ratio, activated vitamin B6, red cell folate, serum vitamin B12, and vitamin D; (d) a visual processing domain comprising visual span, visual speed of processing discrepancy, visual speed of processing, and distance vision on right; and (e) an auditory processing domain comprising reverse digit span, competing words discrepancy, auditory speed of processing discrepancy, and auditory speed of processing; (ii) comparing values for said one or more markers in each of said domains to control values of said markers in subjects not suffering from schizophrenia, schizo-affective disorder or psychosis, wherein the values of said markers indicative of schizophrenia or psychosis are, relative to said control values: - in the neurotransmitter domain, high dopamine, high noradrenaline, and high adrenaline; - in the oxidative stress domain, high urinary hydroxyhemopyrroline-2-one divided by urinary creatinine; - in the nutrition-biochemistry domain, high free copper to zinc ratio (or low zinc to free copper ratio), low activated vitamin B6, low red cell folate, high serum vitamin B12, and low vitamin D; - in the visual processing domain, low visual span, high visual speed of processing discrepancy (percentage of age), low visual speed of processing (percentile), and poor distance vision on right; and - in the auditory processing domain, low reverse digit span, high competing words discrepancy (percentage of pass score), high auditory speed of processing discrepancy (percentage of age), and low auditory speed of processing (percentile). - in the neurotransmitter domain, high dopamine, high noradrenaline, and high adrenaline; - in the oxidative stress domain, high urinary hydroxyhemopyrroline-2-one divided by urinary creatinine; - in the nutrition-biochemistry domain, high free copper to zinc ratio (or low zinc to free copper ratio), low activated vitamin B6, low red cell folate, high serum vitamin B12, and low vitamin D; - in the visual processing domain, low visual span, high visual speed of processing discrepancy (percentage of age), low visual speed of processing (percentile), and poor distance vision on right; and - in the auditory processing domain, low reverse digit span, high competing words discrepancy (percentage of pass score), high auditory speed of processing discrepancy (percentage of age), and low auditory speed of processing (percentile).