Pyruvate and lactate were measured in oviducts during the first 5 days following ovulation in cycling, pregnant, and pseudopregnant mice, to determine how oviductal metabolism might change to promote the availability of these substrates to the early embryo. The postovulatory peak in ampullar pyruvate was most evident in the 12-h pregnant oviduct, 3.19 mmol . kg-1. This increase at +12 h was related to a decrease in lactate dehydrogenase (LDH) activity, compared to cycling animals, observed at this time. Although cycling animals showed a significant increase in isthmic pyruvate at +3 h, no change in isthmic pyruvate was observed in either mated group through the postovulatory period. Isthmic LDH activity was also unchanged in cycling or mated animals through this period. Ampullar lactate in both mated groups was elevated at 12 to 24 h after ovulation, a pattern similar to that seen in cycling animals. Isthmic lactate levels also increased after ovulation in all groups, but in the pregnant group the lactate remained elevated (25-28 mmol . kg-1) through 72 h, while concentrations in the cycling and pseudopregnant animals, returned to low levels (14-16 mmol . kg-1) by 48 h. The patterns of pyruvate and lactate, especially those in the pregnant animals, seem suited to providing these metabolites at levels near those required for optimal in vitro embryo growth. The +12 h ampullar pyruvate peak noted in mated animals implies a specific response to the mating stimulus. Prolongation of increased isthmic lactate levels only in pregnant animals suggests a response of the oviduct to the viable embryo.