Local injection of steroids has been used for some time in the therapy of skin disorders.1-7 Recently, triamcinolone diacetate (9 α-fluoro 16 α-hydroxy prednisolone diacetate) has been found helpful when injected into plaques of psoriasis. There is a marked decrease of the scaling within 1 to 2 weeks, followed by gradual blanching of the erythema of the underlying skin, often with residual depression or atrophy at the site of injection. We have carried out a study to observe the sequential histologic changes found in biopsy sections at intervals of 6 hours to 4 weeks and longer after the injection of a psoriatic plaque with triamcinolone. Three patients have been observed in this study. The patient who was the principle subject was studied intensively with 14 separate biopsies. This case is reported in detail as similar changes occurred in the other patients. Report of Case The patient who was the