We investigated the effects of cadmium (Cd² ) on transcription of the cytochrome P450 side chain cleavage (P450scc) gene and on progesterone synthesis in stable granulosa cells. We used the stable porcine granulosa cell line, JC-410, genetically modified to express a luciferase genomic construct carrying 2320 base pairs (bp) of the P450scc gene promoter (P450scc-2320-LUC). A construct containing only the luciferase gene, pOLUC, was used as a promoterless control. At 1 μM, cadmium chloride (CdCl₂) increased transient expression of P450scc-2320-LUC in JC-410 cells by 2.6-fold after 24-h incubation. A similar pattern of stimulation by CdCl₂ was observed in cells transiently transfected with a luciferase genomic construct carrying 100 bp of the P450scc gene promoter P450scc-100-LUC, whereas no stimulation by CdCl₂ was observed in cells transfected with pOLUC. At 0.6, 1, and 2 μM, CdCl₂ stimulated the activity of the P450scc-2320-LUC promoter in a dose-related fashion by 1.58-, 3.19-, and 2.67-fold, respectively, after 24-h incubation. Northern blot analysis showed that CdCl₂ at 0.1, 1, 2, and 3 μM increased P450scc mRNA levels by 3.13-, 1.38-, 1.61-, and 1.57-fold, respectively, after 24-h incubation. After 48-h incubation, CdCl₂ at 0.6, 1, and 2 μM further increased P450scc mRNA levels by 3.43-, 2.08-, and 2.4-fold, respectively. At 1, 2, and 3 μM, CdCl₂ inhibited progesterone synthesis to 0.48-, 0.38-, and 0.29-fold, respectively. After 48-h incubation, CdCl₂ at 0.1 μM stimulated progesterone synthesis by 1.6-fold. We conclude that Cd² has a dual action in stable porcine granulosa cells: Low concentrations activate, whereas high concentrations inhibit, expression of the P450scc gene and progesterone synthesis. The stimulatory effect of Cd² appears to be mediated via a cis-acting element located 100 bp upstream of the P450scc gene transcription start site.