PURPOSE: Until recently, there has been a limited amount of research comparing functional and anatomical recovery following nerve injury. Previous studies emphasizing anatomical recovery (such as axonal number) have shown that testosterone promotes regeneration in crushed and transected nerves. The purpose of this study was to assess the effect of testosterone on the functional recovery of the sciatic nerve follow-ing a unilateral crush injury. METHODS: Young adult male Sprague-Dawley rats were injected daily with either 500 micro g testosterone proprionate or vehicle alone. The recovery course was followed for six weeks using functional and behavioral testing. Behavioral tests included a footprint gait analysis (as a measure of motor function), response to a skin pinch, and warm water withdrawal (measures of sensory function). RESULTS: Immediately following surgery, all tests indicated complete denervation to the leg distal to the crush site. Anatomical analysis revealed a 22 % increase in the number of axons in testosterone treated animals at 6 weeks post-crush, but no indication of differences in functional recovery. The results of behavioral testing indicated only minor differences in functional recovery as a result of testosterone treatment. CONCLUSION: The results indicate the need for a detailed comparison between anatomical regeneration and functional recovery. An increase in axon number alone may not be an accurate indicator of successful regeneration.