In an attempt to more accurately define the role of the gubernaculum in the descent of the testis, a series of microsurgical procedures was performed in the newborn rat and the incidence of testicular descent was noted 4 weeks later. When the proximal attachment of the gubernaculum to the testis/epididymis was severed, descent occurred in 17 of 17 (100 per cent) of the testes. When the distal attachment of the gubernaculum to the scrotum was severed, 0 of 10 (0 per cent) of the testes descended. When the entire gubernaculum was removed, 0 of 18 (0 per cent) of the testes descended. When the gubernaculum on 1 side and the testis on the contralateral side were both excised, the solitary testis descended into the contralateral hemiscrotum in 34 of 45 (76 per cent) animals. When 1 testis was excised and only the attachment between the contralateral testis and its gubernaculum was severed, the solitary testis was capable of descending into either hemiscrotum. When 1 gubernaculum was completely excised leaving both testes and a solitary gubernaculum present, either 1 or both testes were capable of descending into the hemiscrotum containing the intact gubernaculum. In addition, if a testis was excised prior to normal testicular descent and a silicone prosthesis was placed intraabdominally, the prosthesis was capable of migrating into the scrotum 55 per cent (11 of 20) of the time. These data suggest that in the rat, 1) the gubernaculum with an intact distal attachment is a necessary prerequisite for testicular descent, 2) contraction of the gubernaculum is most likely not the mechanism by which testicular descent occurs and 3) intraabdominal pressure appears to play a major role in testicular descent.