An experiment involving 164 Yorkshire and Hampshire-Yorkshire, first-litter sows was conducted to determine their reproductive performance at first estrus after pig removal on 2, 13, 24 or 35 days postpartum. Average number of days from weaning to estrus decreased linearly (P<.01) as the lactation interval was lengthened. Average time between weaning and estrus was 10.1, 8.2, 7.1 and 6.8 days, for the four groups, respectively. Ovulation rates were not significantly affected by lactation interval.Percent of ova fertilized increased linearly (P<.05) while number of cystic follicles decreased linearly (P<.01) as the lactation interval increased. Average fertilization rates were 81.9, 86.3, 96.5 and 98.0% and cystic follicles per sow averaged 3.3, 1.3, 0.6 and 0.3 for the four lactation groups, respectively. Uterine weight decreased quadratically (P<.05), but uterine length did not change significantly with time following parturition.At 28 days postbreeding pregnancy rates were significantly lower (P<.01) in the 2- and 13-day lactation groups.