The uptake and metabolism of glutamine, production of ammonia and consumption of O2 were studied in kidney slices isolated from mature, gonadectomized and newborn male and female rats in the presence of 0.05, 0.5, 2 and 5 mM-glutamine. Slices isolated from mature intact female rats showed significantly greater conversion of glutamine into CO2 and NH3 without any change in the total uptake of glutamine when compared with all other experimental groups. No difference in O2 consumption was found between mature male and female animals. Ovariectomy reduced glutamine metabolism, NH3 production and O2 consumption without any effect on the total uptake of glutamine. In contrast, castration did not significantly affect glutamine metabolism and production of NH3 but did reduce O2 consumption. Newborn (20- to 21-day-old) rats showed no sex-dependent differences in glutamine uptake and metabolism, production of NH3 and consumption of O2, but values for all these parameters were lower in kidney slices from newborn animals than in kidney slices from mature, intact or gonadectomized male and female rats. It is concluded that in female rats, metabolism of glutamine and production of NH3 may be influenced by ovarian sex hormones.