It has been demonstrated that L-acetylcarnitine (LAC) can enhance the recovery of spermatogonial cells after X-ray damage. In the present work, the effects of LAC on the recovery processes of mouse spermatogenesis after local acute hyperthermia (42 degrees C, 1 hour) was investigated. LAC was administered i.p. (100 mg/kg body weight) every other day for four weeks after heat treatment. At intervals of 8, 14, 21, 28, 35, 40, 45, and 60 days after hyperthermic treatment, testes were weighed and their DNA content analysed by flow cytometry; the round spermatid fraction was found to be higher at 45 days in the LAC-treated animals than in controls (P less than 0.01). Correspondingly, at the same experimental point, the animals without LAC administration showed a lower testicular weight (P less than 0.05). Combined with histological analysis, these results suggest a more rapid recovery of normal spermatogenesis after physical insult with LAC treatment.