Neutrophil chemotaxis in patients with psoriasis vulgaris and psoriatic arthritis was investigated before and after 6 weeks of treatment with zinc sulphate (50 mg elementary zinc three times daily). In patients with active psoriasis vulgaris, a significant increase in neutrophil random migration and directed chemotaxis was demonstrated (10.2 +/- 3.1 and 14.1 +/- 4.1 mu, respectively, greater than that of control patients), while in patients with psoriatic arthritis the values were within the normal range (5.8 +/- 3.2 and 1.1 +/- 4.1 mu, respectively, greater than that of control patients). Although the zinc sulphate treatment had little or no effect on the course of either disease, it restored both the random migration and directed chemotaxis to normal values in psoriasis vulgaris patients. These results support the contention that zinc sulphate modifies neutrophil inflammatory potential; however, the lack of a clinical benefit suggests that neutrophils play only a secondary role in the pathogenesis of psoriasis.