Unilateral resection of the isthmus of the Fallopian tube followed by end-to-end anastomosis of the remaining portions was performed in twenty-one pigs, after which mating took place at known times relative to the onset of spontaneous oestrus. Eggs from both the anastomosed and control tubes were recovered at slaughter immediately following the end of oestrus.

Neither the surgical intervention nor the temporary presence of a tubal catheter influenced the duration of the oestrous cycle. Inhibition or retardation of ovulation found on the side of the anastomosis in three animals was presumed to be associated with the development of postoperative adhesions. As judged by the presence of spermatozoa in the zona pellucida of eggs recovered from thirteen animals, eleven of the tubes were patent above and below the anastomosis. It has been shown that fertilization and early cleavage of pig eggs can take place in the absence of the isthmus, and that the rate of cleavage is not modified by this situation. An increased number of spermatozoa was found on the eggs from the anastomosed tube which, together with the striking incidence of polyspermic eggs (32·4%), indicates that the isthmus normally limits passage of spermatozoa to the upper reaches of the Fallopian tube. Attention is drawn to the implications of these findings in human tubal surgery.