Three general classes of cells were identified in a sample of 460 cells recorded from all areas of the retina subserving the central 40 degrees of vision in the rhesus monkey. 2. One class (colour-opponent) had sustained colour-opponent responses and concentrically organized receptive fields, in which usually one cone mechanism mediated the centre response and one or two different cone mechanisms mediated the antagonistic surround. A few cells of this class had non-concentric (co-extensive) receptive field organization. 3. A second class (broad-band) had transient responses and concentrically organized receptive fields, in which usually two cone mechanisms mediated the centre response. In most cells, the surround had the same spectral sensitivity as the centre and the cells had non-colour opponent responses. In other cells, the surround had a spectral sensitivity different to that of the centre and the cells had colour-opponent responses. 4. The third class (non-concentric) did not have concentrically organized receptive fields. One group of cells had extremely phasic on-, off- or on-off responses and no spontaneous activity, another group had characteristically regular spontaneous activity and was responsive only to moving stimuli. 5. Cells of the colour-opponent class with concentric receptive fields had the smallest centre-sizes, which did not vary markedly from cell to cell (mean 15 mum); cells of the non-concentric class with phasic responses had the largest centre-sizes, which varied from cell to cell. 6. Colour-opponent cells comprised the highest proportion of cells near the foveola; broad-band cells comprised the highest proportion in the more peripheral areas of the retina; non-concentric cells were equally represented in all areas.