Scalp penetration of 7 hair dyes (oxidative and direct) that occurs under conditions of hair dye usage was evaluated for both rhesus monkey and man using 14C labeled materials by quantifying their absorbtion via urine assays. Both species showed a remarkably similar pattern of dye penetration. The extent of scalp penetration is slightly higher for direct dyes but in neither case does it exceed 1% of the applied dose.