The objective of this work was to investigate the effect of oxygen containing terpenes (carvacrol, menthol and carvone) at 5%w/v in hydroalcoholic mixtures (40% ethanol) on the permeation of LHRH across newborn pig skin in vitro. In addition, the amount of LHRH retained in the skin after 24 h of diffusion was determined. It was found that the passive permeation of LHRH was very limited. Although percutaneous absorption of LHRH improved in the presence of the enhancers, a significant enhancement was observed only with carvacrol, an aromatic terpene. The rank order of enhancement ratio for skin permeation was found to be carvacrol > carvone > menthol. The enhancers also affected the retention of LHRH in the skin. The rank order of enhancement ratio for skin retention was carvone > carvacrol > menthol. The results of the in vitro skin metabolism study of LHRH using fresh newborn pig skin showed that the degradation products were detected and the amount of the degraded LHRH increased with increasing duration of incubation time.