Dithranol was incorporated into a hydrogel to develop a slow-release occlusive dithranol therapy for psoriasis. A method of loading the hydrogel with dithranol was developed. Stability of dithranol in the hydrogel was assessed by HPLC assay. Release of dithranol from the hydrogel into an aqueous medium was assessed in vitro. Pilot studies confirmed a comparable irritancy of the resulting dithranol/ hydrogel (DHG) to that of proprietary dithranol preparations. The effect of duration of application was studied in two patients and the rate of dithranol release assessed in vivo. Release from the hydrogel was complete in 14 h. Finally in a clinical study in eight patients comparing the application of DHG with hydrogel alone and conventional dithranol in Lassar's paste, the results of DHG were comparable to conventional treatment and significantly better than hydrogel alone.