Male peacock blennies (Salaria pavo) release odors from their anal glands and, possibly, from their gonads that attract reproductive females. The current study investigated the effects of 11-ketotestosterone (KT) on development of the anal glands, testes, and accessory testicular organs as well as the subsequent olfactory potency of their secretions. After 3 wk of KT treatment (5 mg/kg in silastic implants), clusters of cells secreting neutral mucins differentiated in the anal gland of all treated males, whereas this occurred in only one control male. Secretions by anal glands from KT-treated males elicited greater olfactory responses, as assessed by electro-olfactography, than those from controls. Treatment with KT stimulated testicular gland growth and sialomucin secretion but had no clear effect on the germinal region of the testis; KT also stimulated enlargement of, and fluid secretion in, the blind pouches (paired evaginations of the spermatic ducts). Secretions by the testes and fluid in blind pouches from KT-treated males elicited greater olfactory responses than those from controls. In conclusion, KT stimulates development of the anal glands and testicular accessory organs and promotes odorant secretion, the putative multicomponent male peacock blenny pheromone..