The effect of estrus on the somatic cell count (SCC) of goat's milk was examined by inducing estrus in 24 of 48 seasonally anestrus, lactating dairy goats. Goats were blocked by infection status and ranked on SCC from three preceding herd tests and randomly allocated (within block) to the following three treatment groups: a) "Short," in which an intravaginal progesterone-releasing device was inserted for 12 d plus equine chorionic gonadotropin and dinoprost tromethamine 2 d before device removal (n = 12), b) "Long," in which an intravaginal progesterone-releasing was inserted for 17 d plus equine chorionic gonadotropin on the day of device removal (n = 12), or c) "Control," in which the goats were left as untreated controls (n = 24). Bacteriological status of each gland of each goat was determined before and after synchronization (d -23 and +13) and SCC and milk volumes were determined on d -2, 0, 1, 2, 3, 4, 14, and 25, where d 0 was the day of intravaginal device removal. Goats in the Short group were in estrus before those of the Long group, who were, in turn, in estrus before the Control group. The log10 and log10 absolute SCC (SCC cells/ml x volume) were higher in the Short than in the Control group on d 1, 2, 3, and 4, whereas those of the Long group were higher than those of the Control group on d 2 and 4. These data indicate that estrus resulted in an increase in SCC, and that the increase in SCC was independent of the decline in milk volume at estrus.