Development changes of plastid membrane proteins in C. sativus cotyledons and the effect of benzyladenine (BA) were examined by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Quantitative and qualitative changes of plastid membrane proteins were observed during greening. A protein which became undetectable in the light disappeared following BA treatment in the dark. After illumination BA treatment eliminated the time lag of synthesis of light-harvesting chlorophyll complex proteins observed in the control. In additional illumination, BA conspicuously increased light-harvesting chlorophyll complex proteins in comparison to other plastid membrane proteins.