Clindamycin HCl in a 3% formulation was applied twice daily to the back skin of three white (Yorkshire) and three black (Hampshire) pigs for 22 days. Partial thickness samples of skin were obtained by use of a dermatome on shaved opposite sides at 4 hours and 5 days posttreatment. More than twice the antibiotic activity (P less than or equal to .001) was found in thinner (254 micrometers epidermis) samples than in thicker (1016 micrometers epidermis and dermis, 1 to 3) samples. A significantly higher content of antibiotic (P = 0.015) was retained in the skin of black pigs at five days posttreatment. Groups of ten Upjohn Sprague-Dawley rats were treated similarly with clindamycin phosphate in a 3% formulation three times daily for 22 days. At termination of treatment antibiotic activity was widely distributed, whereas at five days posttreatment residual activity was confined largely to samples of treated skin. No cutaneous irritation due to treatment was observed in either study.