1. Many shallow-water teleosts, e.g. Gobius paganellus and G. ruthensparri, Ctenolabrus rupestris, Lepadogaster gouani and Phoxinus phoxinus, when blinded, show a pigmentary response to photostimulation.
2. This response was analysed quantitatively in Lepadogaster gouani. The melanophores of the blinded animal contract in darkness and expand when illuminated by a 100-watt lamp. In the normal animal on a light background the latter response is checked by a secondary contraction.
3. The dermal response of these fishes is closely comparable to that of the chameleon and it is possible that it may be similarly controlled.
4. No dermal response was observed in adult Pleuronectes platessa.