The effect ofincreased scrotal temperature on semen quality, sexual behavior and the recovery of normal semen production was studied using 3 Pelibuey (OPb) and 3 German Merino (OMP) sheep. An insulated bag was applied to the testicles for a period of six days, during which the average ambient temperature and relative humidity were 23.2±1.ic and 81±2%. Usingan artificial vagina, semen was collected twice weekly for two weeks prior to initiation and once weekly for nine weeks post-treatment. ;. Sexual libido of the rams was measured on the day of semen collection. During the six days of insulated scrotal bag treatment, scrotal (T'E), rectal (T"R) and skin (T"P) temperatures were recorded. Increases ofT'E to 37.1±0.9.C in OPb and 38.2±0.9°C in OMP were registered which decreased (P<0.O 1 )two to three weeks post-treatment. Evaluation of sperm concentration and motility revealed increased seminal pH and an elevated frequency of abnormal and dead spermatozoa, although no change in seminal volume or sexual libido occurred. Breed week interaction was significant (P<0.001) dueto the greater susceptibility of OMP and the early recovery of normal testicular function in OPb. The highly significant (P<0.0001) correlation ofT'E with T'R (r=0.63) and T'P (r=0.65) suggests that the abílity of OPb to compensate the heat effect may be dueto the efficiency ofthe skin in dissipating heat, rather than a thermal regulation mechanism ofthe testicles.