1. By applying atomized chemical solutions on to gecko and carp retinae, neuropharmacological reactions of the photoreceptors and horizontal cells were observed.2. Sodium L-glutamate and L-aspartate, glycine, ACh and GABA, had no appreciable effect on the photoreceptor activity.3. Carp horizontal cells were depolarized by both L-glutamate and L-aspartate. When maximally depolarized, the action of the endogenous transmitter from the receptor terminals was completely masked, resulting in abolition of the S-potentials.4. Responses to red light in both L- and C-type horizontal cells were more strongly affected by aspartate than responses to blue light.5. Glycine and GABA hyperpolarized the horizontal cells, and the S-potentials were diminished.6. ACh had no effect on the activity of the horizontal cells.