Mini rats (Jcl: WistarTGN(ARGHGEN) 1Nts) (MRs) are Wistar rat (WR)-derived transgenic rats in which the expression of growth hormone (GH) gene is suppressed under the presence of antisense RNA transgene. In order to evaluate the effects of GH-deficiency on the acute injury by external stimuli, the dorsal skin responses to a single topical application with 20% hydrogen peroxide (HPO), one of the environmental oxidative stressors, were histologically compared between male MRs and WRs of 8 weeks old, whose hair cycle was under the telogen phase. As a result, formation of granulation tissues, reepithelialization and regrowth of hair follicles were delayed in MRs compared with WRs. While hair follicles of MRs of this age are under a long-lasting telogen phase after their 2nd cycle, a new hair cycle started not only in the HPO-applied area but also in the solvent-applied area with a little time lag. These findings suggest that GH-deficiency may influence the skin responses to the external chemical stimuli.