Corpora lutea from sows at 30, 60 and 90 days of gestation were dissociated enzymically, and the components of the resulting cell suspension were separated by sedimentation at unit gravity. Two luteal cell populations of 30-50 micronm diameter and 15-20 micronm diameter were obtained and superfused for up to 18 h with Dulbecco's modified Eagle medium, the cells being supported in a column in a matrix of Biogel. Fractions were collected every 30 min and assayed for progesterone and oestradiol-17beta. At 30 and 60 days of gestation the large luteal cells produced progesterone at an initial rate of approximately 100 ng/h/10(5) cells, which decreased to half this rate at 90 days. The smaller cells also released progesterone into the medium at approximately 15-20 ng/h/10(5) cells at all stages of gestation. At 30 days of gestation, neither cell type released significant amounts of oestradiol-17beta, but from 60 days onwards ,significant and increasing quantities were measured in the superfusates from the larger cells. Both cell types were perfused with porcine LH at the three stages of gestation, and both showed an immediate response in terms of progesterone release which decreased in magnitude with increasing age of gestation. The response of the smaller cells was greater than that of the larger cells.