Radiometric biochemical assays were carried out for choline acetyltransferase (ChAc) and acetylcholine esterase (AChE) in retinas isolated from 90-day-old pigmented mice. The retinas were either normal [(C57Bl (6) and rd/le controls)], or genetically receptorless (rd/le and C3H), or had markedly reduced inner layers due to postnatal treatment of C57Bl (6) mice with monosodium glutamate. The receptorless rd/le retinas were obtained from an inbred hybrid stock that provided littermate contols with normal retinas. Glutamate-damaged retinas were compared to retinas from untreated control animals. Receptorless C3H retinas were compared to both sources of normal retinas. Control retinas had specific activities (millimoles per kilogram dry weight per hour) of 36.5 to 38.5 for ChAc and 2,180 to 2,350 for AChE and total activities per retina (nanomoles per hour) of 23 to 26 for ChAc and 1,360 to 1,160 for AChE, with the higher total values coming from slightly heavier rd/le controls. Receptorless retinas had 44 to 48 times the ChAc specific activity of those from glutamate-treated animals and had 2.4 to 2.5 times that of retinas from control animals. They had five to six times the AChE specific activity of retinas of glutamate-treated animals and 2.4 to 2.5 times that of controls. On a total activity per retina basis, receptorless rd/le retinas had 81 per cent of the ChAc activity and 66 per cent of the AChE activity of those from littermate controls and receptorless C3H retinas had 97 per cent and 98 per cent of the total ChAc and AChE activity of the C57Bl (6) controls, but only 91 per cent and 82 per cent of the same total activities in the heavier rd/le controls. The data are consistent with the view that both enzymes are normally more concentrated in the inner than outer retina, with the disparity being more marked for ChAc.