In verebrate retina melatonim (MEL) level and activity of serotonim N-acetyltransferase (NAT; a key regulatory enzyme in MEL biosynthetic pathway) fluctuate with a light-dependent circadian rhythm, with peak values at night. The nocturnal increase of MEL synthesis is dramatically suppressed by acute exposure of animals to light. Experimental evidence suggest that the inhibitory effect of light on the MEL-generating system in retina is mediated. at least partially, by dopamine (DA) acting on D2-like DA receptors (2,3). In this work we verified a subtype of DA receptors regulating NAT activity in the retina of chick.