Spermatogenesis requires the presence of functional somatic Sertoli cells in the seminiferous tubules of the testis. Sertoli cells provide support and factors necessary for the successful progression of germ cells into spermatozoa. Sertoli cells are regulated to a large degree by the glycoprotein hormone FSH, which is required for the testis to acquire full size and spermatogenic capacity. Signaling events initiated by the binding of FSH to its receptor lead to an alteration of Sertoli cell gene expression. To characterize the changes in gene expression in FSH-treated Sertoli cells, we used the mRNA from these cells to screen Affymetrix U34A rat GeneChip oligonucleotide microarrays. Sertoli cells from 20-d-old rats were cultured in the presence of 25 ng/ml ovine FSH. At 0, 2, 4, 8, and 24 h after the addition of FSH, total RNA was purified and used to prepare biotinylated target, which was hybridized to the U34A rat microarray containing approximately 9000 rat genes. Analysis identified 100-300 transcripts at each time point that were up-regulated or down-regulated by 2-fold or greater. Genes previously reported to be FSH or cAMP regulated in rat Sertoli cells were identified, in addition to numerous genes not reported to be expressed or FSH regulated in Sertoli cells. The expression patterns of five of these genes, encoding nerve growth factor inducible gene B, PRL-1, PC3 nerve growth factor-inducible antiproliferative putative secreted protein, diacylglycerol acyltransferase, and an expressed sequence tag, in FSH- and N,O'-dibutyryl cAMP-treated rat Sertoli cells were confirmed and characterized by Northern blot analysis. Thus, we have begun to define the transcriptome induced and repressed by FSH in rat Sertoli cells, and we have generated datasets of genes available for further analysis in regard to spermatogenesis and Sertoli cell signaling.