The involvement of central biogenic amines in the mechanisms controlling photoperiodically induced testicular development in Coturnix quail were studied employing pharmacological approaches. Daily administration of alpha methyltyrosine (MT), which blocks catecholamine (CA) biosynthesis, to 6 wk old quail exposed to long daily photoperiods markedly depleted brain dopamine (DA), norepinephrine (NE) and epinephrine (E). This was associated with a partial suppression of testicular growth 7 days after light stimulation. Combined treatment with MT and L dihydroxyphenylalanine (L-DOPA), a precursor of DA, NE and E, elevated the monoamine levels in the brain and prevented the bloskein effect of MT on testicular growth. Selective blockade of NE and E biosynthesis with diethyl dithiocarbamate (DDC) depleted both NE and E, while it elevated DA level. Furthermore, such treatment reduced testicular weight. In DDC treated birds D,L dihydroxyphenylserine (DL-DOPS) administration, which bypasses the DDC block, restored only brain NE level and reversed the blocking action of DDC on testicular weight. It is concluded that central NE plays a role in transformation of the photoperiodic information affecting gonadal development in Coturnix quail.