['Previous research from this laboratory has suggested that a relationship exists between the increase in circulating progesterone concentrations at the time of hCG administration and cycle outcome in patients undergoing IVF. Progesterone (P) increases of threefold or better within the 24-h period surrounding hCG administration appeared to be associated with a higher pregnancy rate. These data suggest a functional difference in the luteinized-granulosa of patients undergoing IVF. To test this hypothesis:', 'A split-split plot arrangement of treatments with two cell sources under five hormonal stimulations at four time points.', 'Luteinized-granulosa cells (LGC) were collected from patients with either a normal increase (> or = threefold = NC) in circulating P (n = 4) or those with lower P increases (AC; n = 4). The cells were isolated by Ficoll gradient centrifugation and then cultured in 24-well culture plates using a modified media 199 containing 100 mIU/ml of hMG, FSH, LH, hCG, or a nonhormonal control to stimulate steroid-hormone production. At time points 2, 4, 6, and 8 days, media from each well was frozen for later hormone assay and replaced with fresh media containing the same stimulating factor. After all the media had been collected, P and estradiol (E2) released into the media were measured using radioimmunoassay.', 'Results indicate a higher media concentration of P (P < 0.001), but not E2 (P = 0.254), from NC, regardless of hormone stimulation or time in culture, when compared to the media from AC. Media concentrations of E2 were affected by a cell source by hormone stimulation by time interaction (P < 0.001) with varying effects. Media from NC maintained a constant E2 of between 1000-3000 pg/ml over the 8-day period (P = 0.163). However, media from AC demonstrated a stimuli-dependent E2 release (P < 0.001) ranging from < 1000 to over 11,000 pg/ml.'] Does hormone release from cultured luteinized-granulosa cells mimic differences seen in vivo in patients undergoing IVF-ET?