The aim of the study was to investigate the impact of operant conditioning on the receptor pattern in the visual cortex of calves. A reward paradigm was used to induce conditioned preference for colours. Binding sites in visual cortex specimens from conditioned and naive animals were assayed in vitro on cellular basis after dissociation of the tissue by collagenase, incubation with fluorescent ligands and flow-cytometry for fluorescence analysis. The cellular counts were subdivided according to sedimentation at 200 g as well as via the flow-cytometrical histogram by size and granularity. Binding sites of dopamine D1 and D2 receptor subtypes, glucocorticoids, opioids, casein as well as glycine and N-methyl-D-aspartic acid (NMDA) were detected by fluorescent molecular probes. In displacing naloxone fluorescein from NMDA- and mu-opioid receptors NMDA and meth-enkephalin were used. Comparisons between portions of fluorescent cellular counts from visual cortex tissue of conditioned and naive animals revealed a small increase (1.2-fold, P < 0.05) in opioid receptors of large and high granulated counts, bearing > 80% D1 receptors, and a decrease (0.70-fold, P < 0.05) in less granulated counts with variable portion of D1 receptors. Conditioning resulted in higher and lower displacing rates by meth-enkephalin and NMDA, resp., and in a reduce in counts with dopamine D1 (0.8-fold, P < 0.05), glycine and glucocorticoid binding sites (0.6-fold in both cases, P < 0.01). A tendency of elevated phagocyte marker expression occurred in high granulated counts. The data suggest that conditioning is accompanied with significant and in part marked change in binding sites studied. Induction of scavenger activity may parallel this process. As cellular portion with glycine and glucocorticoid receptors were most markedly altered by conditioning, the neurochemical needs of the used paradigm seem to focus to motility-related functions.