Following artificial hibernation, sexually mature male garter snakes ( Thamnophis sirtalis parietalis) exhibited a decline in courtship behavior irrespective of castration, sham operation, or castration with testosterone replacement therapy. Behavior declined more rapidly in castrated animals with testosterone replacement than in castrated or sham-operated animals. In sham-operated animals, the decline in courtship was accompanied by changes in testicular weight and spermatogenic state from small spermatogenically inactive testes to large spermatogenically active testes. Serum androgen levels were more than fourfold greater in sham-operated animals than in castrated animals; cell height of the androgensensitive renal sex segment was greatest in castrated animals with testosterone replacement and least in castrated animals. These findings indicate that following artificial hibernation, male courtship behavior of T.s. parietalis is independent of the presence of the testes.