ABSTRACTThe dorsal resting hair of C3H mice was shaved, activating the hair into the anagen stage. Hair regrowth in mice of different ages (10–20 mice in each group), whose hair cycles were in the telogen stage, were compared after shaving. In both groups of mice, new hair growth was not uniform, but irregular on the shaved areas. Delay in hair regrowth increased as the mice became older (20<66<188<312 day old mice). Furthermore, eighteen 59 day‐old mice were used for biochemical analysis. Nine days after shaving, 30–50% of the shaved skin area was covered with new hair. After sacrifice, the dorsal skins were separated into hair re‐growing, non‐growing, and non‐shaved control areas. Several enzyme activities in the extracts from the above‐named areas were compared in terms of “per g of wet weight tissue”, “per mg DNA” and “per mg of soluble protein”. The activities of ornithine decarboxylase (ODC), transglutaminase (TGase) and alkaline phosphatase (Al‐P) were remarkably high in the extract from the hair re‐growing area as compared with that from the non‐growing area. Comparison of the activities of the follicle‐rich fractions from the hair re‐growing area to those of the non‐shaved area showed that ODC, TGa