A group of 40 patients was collected to study the possible existence of systemic toxicity secondary to the use of topically administered anthralin. Creatinine clearance, chemistry profile, complete blood cell count, and urinalysis performed on all patients before treatment and after one and three months of continuous topical anthralin therapy indicated no evidence of systemic toxicity in any patient. No change in renal function studies in two anthralin-treated patients with renal disease suggests that even renal disease is not necessarily a contraindication to the use of topically administered anthralin in low concentrations for treatment of psoriasis.