The glyoxylic acid technique for fluorescence histochemical characterization of catecholamine neurons has been used to visualize the catecholaminergic cells and processes in the rat retina. Incubation experiments with exogenous amines and with or without a selective inhibitor of amine uptake, showed that only dark-adapted rat retina was able to take up exogenous amines in vitro, after depletion by α-methyl-p-tyrosine.