Radiotherapy for cancer produces prolonged testicular damage that is manifested by failure of spermatogenic recovery following treatment. It has thus become important to develop methods to induce the recovery of spermatogenesis, if fertility is to be restored in patients (De Vita et al., 1997). The importance of steroid hormones in the control of testicular function has lead to numerous studies being conducted on the use of these hormones as treatment to protect the testes from radiation damage (Desjardins and Ewing, 1993; Kurdoglu et al, 1994; Kangasniemi et al., 1996a; Shuttlesworth et al., 2000). x The aim of this study was to investigate the effects of low dose gamma irradiation on the rat testes and the use of testosterone to reverse damage to the testes resulting from radiation exposure. Sprague Dawley rats were subjected to irradiation doses of 3.5 and 6.0 Gy. The rats were treated with testosterone over 4 and 8 weeks. Analyses were carried out at three levels: histological, kinematic, and endocrine. Irradiation led to a dose dependent reduction in spermatogenic cell numbers. Percentage sperm motility was decreased, and two of the five measured kinematic parameters, curvilinear velocity and straight line velocity, were decreased. Luteinising hormone (LH) and follicle stimulating hormone (FSH) concentrations increased in a dose dependent manner, while testosterone concentration showed insignificant fluctuations. Following testosterone administration, spermatogenic cell numbers improved. LH concentrations were restored to almost control levels. Testosterone administered following exposure of the rat testes to low dose gamma irradiation led to the recovery of spermatogenesis.