The number of sperm per collection was followed for one year in swine exposed to 0, 300, 600, and 900 r of local testicular irradiation. The general response pattern in swine conforms to that outlined for other mammals. About 60 days has been estimated as the interval from primary spermatocyte to sperm in the ejaculate. The general recovery pattern, as measured by sperm number per collection between 70 and 300 days, is linearly related to dose on a logarithmic plot, suggesting that recovery is a function of the number of surviving spermatogonia. The length of time required for recovery to fertility appears to be longer in swine than in mice.