To characterise PCBs action on luteal cell steroidogenesis and cell viability two PCB congeners were selected as model substances. PCB 126 because of its dioxin-like configuration and high toxicity while 153 because it is one of the most commonly detected congeners in breast milk. Luteal cells collected from mature corpora lutea were cultured in M199 medium at 37 degrees C. Control cultures were maintained in that medium alone, while other cultures were supplemented with either PCB 126 (5, 10, 50 and 100 pg/ml) or PCB 153 (5, 10, 50 and 100 ng/ml). After 24 h, 48 h and 72 h of culture media were collected for P4 content analysis. Cell viability was measured using LDH cytotoxicity test. Exposure of luteal cells to all doses of PCB 126 for 24 h had no effect on progesterone secretion while longer, 48 h and 72 h exposure decreased progesterone secretion in a statistically significant manner. Concentration dependent decrease in progesterone secretion by luteal cells was seen after 24 h and 48 h exposure to PCB153 while concentration dependent increase in progesterone secretion was noted after 72 h exposition to this congener. The toxic effect of both congeners was observed only after 72 h exposition to 50 pg/ml and 100 pg/ml in the case of PCB 126 and 50 ng/ml and 100 ng/ml in the case of PCB 153. In conclusion, these results suggest that there are differences in PCB 153 and 126 action in luteal cells. Since information concerning mechanism of PCBs action on luteal cells is scarce, these preliminary experiments are of pioneering character.