We assess the percutaneous penetration potential of two commercially distributed semipermanent hair dyes. Utilizing several solvent systems in conjunction with thin-layer chromatography (TLC), we found that the commercial formulations contained at least nine component chemicals. Eight adult volunteers had their hair dyed with these preparations and 24-hour urine specimens were collected daily for five days. The urine was lyophilized and extracted with diethyl ether under acid and alkaline conditions. The TLC of urine from four of the eight subjects, taken from one to four days after dyeing the hair, disclosed a purple spot. This spot, though not identified, was the same with both dye preparations. It is likely that these hair dyes not uncommonly penetrate the skin.