The gonadal and accessory organ atrophy following transfer of male hamsters from long (LP) to short photoperiod (SP) is preceded by reduced prolactin secretion and involves reductions in hypothalamic LHRH release and catecholamine turnover. These experiments examined the temporal aspects of changes in medial basal hypothalamic/median eminence (MBH/ME) catecholamine turnover rates in male hamsters undergoing SP-induced gonadal atrophy. Hamsters were sacrificed at three, six, nine and twelve weeks of SP exposure. MBH/ME catecholamines and indoleamines were determined by high performance liquid chromatography coupled with electrochemical detection. Reductions in serum prolactin (PRL) levels and increased MBH/ME dopamine (DA) turnover rates were observed at three and six weeks of SP exposure. Both steady state concentrations and turnover rates of norepinephrine (NE) and DA were depressed after nine and twelve weeks of SP exposure, at which time testicular and accessory organ atrophy had occurred. Serotonin (5-HT) and 5-hydroxy-3-indoleacetic acid (5-HIAA) concentrations were insignificantly changed during the period of SP treatment but the 5-HIAA/5-HT ratio was significantly increased after six weeks of SP exposure. It was concluded that increased MBH/ME DA turnover represents an initial, SP-induced neuroendocrine event. This increase in DA turnover probably contributes to the reduced PRL secretion which precedes, and may play a role in the ensuing gonadal and accessory organ atrophy.