The retinal circuitry of S cone pathways, and the receptive field properties of subcortical (lateral geniculate nucleus - LGN) neurones with S cone input were measured in marmosets (Callithrix jacchus). Many features of S cone pathways in marmoset retina are comparable with those described for other primate retinas such as macaque monkeys. The S cones make invaginating (''ON'') type contacts with blue-cone bipolar cells, which in turn co-stratify with a small-field bistratified (''blue-on'') ganglion cell type. In contrast to a recent report from macaque retina, however (Klug et al., J Neurosci, 2003), there was no evidence for contact of ''OFF'' type from midget bipolar cells in marmosets. Recordings from the LGN confirmed that the majority of S-cone input neurones are ''blue-on'' type; the blue-on cells are predominantly located in the koniocellular division of the LGN. Receptive fields of ''blue-off'' type were less frequently encountered. The ''blue-off'' cells were segregated to the koniocellular layers. Receptive field centre diameters of blue-on and blue-off cells were larger (by four - to twenty-fold) than those of parvocellullar cells at equivalent visual field eccentricities. These data suggest that S cone signals contribute to wide-field ganglion cell types in the retina, and travel through the koniocellular layers of the LGN, in marmoset monkeys.