Short-term changes in renal function, blood pressure, and electrolyte levels in patients receiving cyclosporine for dermatologic disorders. We compared the changes in renal function, blood pressure (BP), and concentrations of serum potassium, magnesium, and urate (uric acid) in two groups of patients not given transplants. Group 1, comprising 21 psoriatic patients, was treated with 14 mg/kg per day of oral cyclosporine for 4 weeks in a prospective, placebo-controlled study; group 2, comprising 28 patients with diverse cutaneous diseases, was given 6 mg/kg per day of oral cyclosporine for 1 to 3 months in a prospective, open-labeled study. Renal function (determined by serum urea nitrogen [SUN] and creatinine levels and urinalysis), BP, serum electrolyte levels (potassium and magnesium), and urate level were measured weekly for the first 4 weeks in both groups, and then, after 2 and 3 months of therapy, in group 2 only. During the first 4 weeks in group 1 patients, there were significant increases in values of SUN, creatinine, BP, potassium, and urate, and a significant decrease in the serum magnesium value. When data for the two groups were combined, the changes from pretherapy values in each of the above measures (except systolic BP) during the first 4 weeks correlated significantly with cyclosporine trough levels. In group 2, the changes that occurred in the first 4 weeks in the SUN value, SUN/creatinine ratio, and BP were magnified over the subsequent 8 weeks of treatment. In the combined group for the first 4 weeks of therapy, duration of therapy, independent of cyclosporine trough levels, correlated with changes in SUN, creatinine, and urate levels, but not with changes in the potassium or magnesium level or in BP. We conclude that the cyclosporine blood level was a better discriminant than cyclosporine dosage in the analysis of renal dysfunction and hypertension in these patients. 