Female rats, 5 days of age, received micropellets of a testosterone-propionate (TP)-paraffm mixture in the brain or under the skin, pellets of paraffin alone in the brain, or no treatment. The only animals that developed the acyclic, anovulatory syndrome as adults were those that had TP implanted in the brain. The most effective site for producing the syndrome was the ventromedial-arcuate area of the hypothalamus. The shortest latencies to onset of the syndrome occurred in animals with TP at the anterior portion of the arcuate nucleus.