Male Holtzman rats were given a vitamin A deficient (VAD) diet from 21 days of age and retinoic acid after the onset of vitamin A deficiency. At 130 days of age, seminiferous tubules contain Sertoli cells, spermatogonia and preleptotene spermatocytes; serum LH and testosterone values are low normal, while FSH levels are high. Oral feeding of a single dose of 1 mg vitamin A (followed by a regular commercial rat pellet diet) causes reinitiation of spermatogenesis, although testosterone remains low and FSH does not return to normal for 60 days. After vitamin A treatment (PVA), kinetic characteristics based upon histologic criteria of the reinitiated spermatogenesis in VAD rats were normal. Pachytene spermatocytes can be seen by Day 14 PVA and spermatids by Day 24 PVA; elongation of spermatids was completed by Day 31 PVA and spermatozoa were formed by Day 41. Quantitatively, sperm production remained below normal at 150 days PVA, although epididymal sperm counts had continued to increase PVA to 50% of that in mature controls. The qualitative normalcy of spermatogenesis in PVA-VAD rats was demonstrated by fertility with normal litter size. Thus, VAD causes reversible germ cell depletion. Reinitated spermatogenesis in the VAD rat provides a kinetically normal, in vivo system in which functionally normal spermatozoa are produced and in which it may be possible to study the biochemical and morphological events of specific stages of spermatogenesis.