An investigation has been made on the effects of short exposures to low intensities of blue; red, far-red, and white light, seperately and in certain combinations, on primary leaf growth and on the activities of some chloroplastic and cytoplasmic enzymes of dark-grown beans. Three distinct types of promotive response have been reccognized. (i) one dependent on the formation of phytochrome-730 (p730). (ii) another dependent on one (protochlorophyll) or more non-phytochrome red-absorbing susbstances, and (iii) a positive interaction of successive treatment with red and blue light. Only the photocon version of protochlorophyll appears to be a photoresponse specific to the plastids. As the other responses show effects of equal magnitude on both chloroplastic and cytoplasmic components and as P730 induces considerable leaf growth the sites of the primary responses are probably not located in the plastids.