The efficacy and pharmacokinetic profiles of two oral formulations of cyclosporine A (Sandimmune and Neoral; Sandoz Pharmaceuticals, East Hanover, NJ) were evaluated in 37 patients with moderate to severe plaque psoriasis in a randomized, double-blind, modified, crossover study. Cyclosporine A (150 mg twice daily), administered in either formulation, reduced the severity of plaque lesions: 94% of all patients reported at least moderate improvement and 70% reported complete clearing. Approximately 2 weeks of therapy were required for drug exposure to stabilize on either formulation. Cyclosporine A exposure from Neoral was significantly greater relative to that from Sandimmune across all study weeks. At the eighth week (before crossover), AUC and Cmax values for Neoral and Sandimmune were 5618 +/- 1705 versus 3202 +/- 596 ng.h/mL and 1283 +/- 337 versus 623 +/- 173 ng/mL, respectively. In crossover analysis at steady state, the relative oral bioavailability of cyclosporine from the Neoral formulation was 54% greater than that from Sandimmune. Some pharmacokinetic parameters showed less variability both between and within groups of patients taking Neoral versus Sandimmune. Both formulations were well tolerated, in that most adverse events were of mild severity.