Diphencyprone (DPCP) is a contact allergen used in immunotherapy of alopecia areata. Its effect on normal mouse hair growth, however, has not been reported. In this study BALB/C mice were sensitized by a single painting of DPCP (2%) on one side of the shaved back. Eczematous reaction appeared 3-5 days after application. The mice were rechallenged with 0.1% DPCP 1 wk after sensitization. Increased hair growth rate was observed in about 30% of the mice 48 hrs after elicitation. The plucked hair on the sensitized side was much longer than the control side (3.6±0.4 vs 1.2±0.3mm, P<0.05, Student's t-test). Histologically, downward elongation of hair follicles and thickness of epidermis and diffused lymphocyte infiltration were seen at 48 hrs after elicitation. About a week after elicitation all mice showed longer hair in the sensitized side than the control side. PKC isoform levels in normal and DPCP sensitized skin in the induction phase and rechallenge phase were measured by Western blot. PKC α,γ,δ,θ and ε were decreased in both phases (1.5-2.2 times decrease, P<0.05-0.02) while β and τ were unchanged. These results indicate that DPCP has a hair growth promotion effect in normal mouse and that PKC isoforms may play a role in DPCP enhanced hair growth.