Both animal and clinical studies have demonstrated that progesterone has antiepileptic properties. Progesterone in the immature, but not mature brain, markedly inhibits kindling. The purpose of this study was to determine if the kindling inhibition effect of progesterone is related to systemic endocrine properties. The effect of alphaxalone and alphadalone acetate, two progesterone-like compounds devoid of significant endocrine effect, were administered to both immature and mature male rats during kindling. Alphaxalone and alphadalone acetate markedly inhibited kindling in the immature rat, but had minimal effects in the mature animal. This study demonstrates that the kindling inhibition effects of progesterone are not dependent on systemic endocrine properties.