SummaryThirty‐four patients with originally extensive psoriasis, for whom topical mustine treatment had been instituted more than one year previously, were successfully followed up.That the high allergy rate does not preclude the usefulness of this form of therapy in selected cases is well shown. Seventy‐one percent had a good result and over 50 per cent needed only occasional applications for ready control and use mustine as their treatment of choice. Forty‐seven percent developed allergy but 63 per cent of these were desnsi