Abstract. Cotyledons of etiolated gherkin seedlings do not turn green upon transfer to high intensity red light (about 25 W/m2). A pre‐irradiation with high intensity red light has an after‐effect as chlorophyll accumulation during a subsequent exposure to white light (20 W/m2) is inhibited. The capacity of protochlorophyll regeneration during a dark period depends on the length of a previous light period but is hardly affected by the light intensity. At high intensity light the rate of protochlorophyll regeneration, which also depends on the length of the foregoing irradiation, is lower than that at low intensity light only during the first 1.5h of the light period. It is concluded that high intensity red light inhibits chlorophyll accumulation mainly by photo‐bleaching of chlorophyll. The after‐effect is the result of a photooxidation which may lead to photo‐bleaching of newly formed chlorophyll in relatively low intensity light. Photoinhibition of chlorophyll accumulation is accompanied by a disturbed development of etioplasts into chloroplasts.