1. Nine hundred and sixty cat retinal ganglion cells were evaluated with respect to receptive-field organization and latency to antidromic activation of their axons from optic-tract and mid-brain positions.2. The vast majority (92%) had the familiar concentric centre/surround organization. As in earlier work these could be classed as sustained or transient, independently of the centre type. About 13% of the concentric cells were characterized by relatively sluggish responses to conventional visual stimuli which yielded brisk responses from the others. The sluggish cells constituted a previously unspecified class of concentric receptive fields.3. The responses of brisk and sluggish cells to a variety of stimuli were described with a view to developing procedures for distinguishing them on functional grounds.4. Measurements of latency to antidromic activation of retinal axons confirmed earlier work in showing that cells classed as brisk-transient had the shortest conduction times from the optic tract. Cells classed as brisk-sustained had intermediate conduction times and from earlier work would constitute an important input to the lateral geniculate nucleus. A proportion of the brisk-sustained axons reached the pretectal region (especially on-centre types) and a small minority reached the superior colliculus (especially off-centre types).5. Sluggish cells had generally slower antidromic conduction times; despite some overlap with the brisk-sustained class, the slower conduction provided independent support for the functional differentiation. Sluggish axons reached the pretectal region and superior colliculus.6. The brisk-sustained cells constituted the majority of the recordings in the area centralis.7. A comparison with the morphological data of Boycott & Wässle is made which suggests that the brisk-transient units corresponded with alpha cells, the brisk-sustained with beta cells, and the sluggish units were included amongst the gamma cells.