At a concentration of 4 mg/ml chloramphenicol does not affect the formation and fine structure of prolamellar bodies. It also does not inhibit their light-induced loss and conversion into thyllakoids. It does, however, strongly affect the aggregation of thyllakoids into grana, most likely by retarding or interrupting some process(es) vital to the orderly assembly of thyllakoids. These results are discussed in light of the known effects of chloramphenicol on formation of pigments, electron-transfer and fraction I protein, and plastid membranes. It is suggested that the aggregation of thyllakoids into grana in higher plants may be regulated by some protein(s) synthesized by the plastid ribosomes, whereas the formation and maintenance of prolamellar bodies as well as the synthesis of plastid membranes may be regulated by protein(s) synthesized in the cytoplasm.