['Severity in psoriasis and atopic dermatitis (AD) is commonly assessed with the Psoriasis Area and Severity Index (PASI) and the SCORing Atopic Dermatitis (SCORAD), respectively. Until today no serum marker is available to reflect the clinical scoring in both diseases. As mast cells play an important role in the pathogenesis of early psoriasis and AD, tryptase, a major compound of mast cell granules that is released upon activation, could in principle serve as such a marker.', 'To assess the correlation between serum tryptase and severity of psoriasis and AD as well as the correlation between total IgE levels and severity of AD.', 'Serum samples from patients hospitalized for psoriasis and AD were collected at time of admission and time of discharge from hospital. PASI and SCORAD assessments were performed at the same time points. Outpatients presenting with naevi and other benign noninflammatory skin lesions served as control group. Serum tryptase values and total IgE levels of patients with AD were measured using a fluoroenzyme immunoassay technique.', 'No correlation of serum tryptase level with either the severity of psoriasis or the severity of AD was seen. Total IgE levels in patients with AD at time of admission and discharge from hospital remained the same.'] Is serum mast cell tryptase a useful marker for disease severity in psoriasis or atopic dermatitis?