The process of luteinization, during which granulosa cells are transformed into luteal cells, is accompanied by dramatic changes in the response of luteal cells to LH. Although luteal cells require LH-cAMP signalling cascade for survival, whether these cells respond to trophic factors through changes in gene expression remain poorly characterized. In an attempt to characterize gonadotropin (LH)-regulated gene expression in the bonnet monkey corpus luteum (CL), changes in gene expression after GnRH antagonist treatment to inhibit LH secretion, different stages of CL and during hCG-simulated early pregnancy were examined using DDRT-PCR, Northern blot and semiquantitative RT-PCR analyses. We have identified 7 non-redundant cDNAs whose expression were regulated by LH. The results show that inhibition of LH secretion not only leads to down-regulation in the expression of genes viz., LDL receptor and Aldose reductase, but expression of some of the genes was up-regulated viz., Humanin, RNA helicase, Lyric protein, Acidic ribosomal phosphoprotein and KIAA1750. Messenger RNA levels of the genes identified as up-regulated after LH inhibition were higher during late- compared to the early- and mid-luteal phase CL, but treatment with hCG down-regulated their expressions. We conclude that we have identified novel genes (known and unknown) that are up-or down-regulated by LH, and the results suggest that LH-mediated activation and repression of expression of many genes is central to the regulation of structure and function of CL in the monkey.