Investigations were conducted on the in-vitro metabolic activity of rabbit testicular tissue after exposing the testis to abdominal temperatures for 2, 6 or 24 hr. Metabolic activity increased with the shorter exposure and then significantly decreased as compared with that of normal testicular tissue. Tissue treated in this way recovered its normal metabolic activity when subjected for 30 min to an ice-cold glucose solution. Tissues exposed to abdominal temperature for 24 hr were found to contain 12% less glucose and 27% less lactic acid than control tissues. This study suggests that spermatogenic arrest which results from exposure of the testis to elevated temperatures may be caused by reduced levels of substrate in the tissue.