Summary.The threshold of retinal on/off‐elements, isolated by the micro‐electrode technique in the cat retina, have been determined for three wave‐lengths as test light, a red, a green and a blue, before and after adaptation to one of three adapting lights, Ilford spectral green, blue or red.Statistical threshold correlations were calculated. Blue and red as well as blue and green proved to be independent for on‐ and off‐component, but there was a negative correlation of ‐0.46 between Green on‐components and Red off‐components, signifying that a certain number of the elements, responding best to green at onset could not respond to red at cessation of illumination, as would be required by a mechanism of contrast.Adaptation with the three adapting colours was found to give a number of highly selective and extremely variable effects in terms of the three test lights.The amount of depression, caused by coloured adaptation, was found to depend on the off/on‐ratio in such a fashion that the on‐sensitive elements tended to loose sensitivity at ‘on’, the off‐sensitive at ‘off’.For some elements the off/on‐ratio was found to increase towar