At least in mammals, retinoic acid is a pivotal factor in maintaining the functionality of the testis, in particular, for the progression of germ cells from mitosis to meiosis. Removal of dietary vitamin A or a targeted deletion of retinoic acid receptor alpha gene (Rara), the receptor for retinoic acid, in mice, led to testicular degeneration by a dramatic loss of germ cells and a loss of control of the spermatogenic cycle. The germ cells that remained in the vitamin A deficient (VAD) rat testis were spermatogonia and a few preleptotene spermatocytes. Spermatogenesis can be reinitiated by injection of VAD rats with retinol, the metabolic precursor of retinoic acid, but to date, the functions of retinoic acid in the testis remain elusive. We have applied DNA microarray technology to investigate the time-dependent transcriptome changes that occur 4 to 24 h after retinol replenishment in the VAD rat testis. The retinol-regulated gene expression occurred both in germ cells and Sertoli cells. Bioinformatic analyses revealed time-dependent clusters of genes and canonical pathways that may have critical functions for proper progression through spermatogenesis. In particular, gene clusters that emerged dealt with: (1) cholesterol and oxysterol homeostasis, * (2) the regulation of steroidogenesis, (3) glycerophospholipid metabolism, (4) the regulation of acute inflammation, (5) the regulation of the cell cycle including ubiquitin-mediated degradation of cell cycle proteins and control of centrosome and genome integrity, and (6) the control of membrane scaffolding proteins that can integrate multiple small GTPase signals within a cell. These results provide insights into the potential role of retinoic acid in the testis.