1. Receptive field centres of 144 sustained and transient retinal ganglion cells were mapped in cats under light pentobarbitone anaesthesia.2. Sustained on-centre, sustained off-centre, transient on-centre and transient off-centre cells had different mean sizes of receptive field centre, with some overlap between their distributions.3. For each class of cell, central fields had the smallest field-centres; progressively larger field-centres were encountered more peripherally.4. All classes of ganglion cells tended to have slightly elliptical receptive field centres. Major axes of over half of all receptive fields were oriented within 20 degrees of horizontal. These trends were independent of pupil dimensions, or of receptive field eccentricity or position in the visual field. The results almost certainly reflect asymmetry in retinal wiring.5. Two cells of thirty-nine tested were sensitive to axis of motion; in both cases the preferred and major axis were horizontal. A further cell was orientation specific.