In cell cultures derived from anterior pituitary glands of rats, enzyme activities of cell homogenates and hormone (GH, PRL, LH, and FSH) content of the culture media were measured. Sex differences in enzyme activities representing major metabolic pathways (citrate cycles, pentose cycles, and glycolysis) were demonstrated both in freshly dispersed cells and in 8-day-old cultures; in cultures of both sexes enzyme activities increased during cultivation. In cultures derived from female rats, cell protein doubled by the 12th day and remained constant for up to the 24th day in culture, whereas enzyme activities showed changes suggesting that cell metabolism shifted to anaerobic glycolysis during cultivation. In the culture media the presence of four pituitary hormones was demonstrated for as long as 3 weeks of cultivation with variable secretion dynamics; the release of gonadotropic hormones diminished gradually whereas that of GH remained constant and PRL levels increased with time. These results indicate that under strictly defined culture conditions pituitary cells may function in spite of profound metabolic changes.