Comparisons of proteins synthesized in photoperiodically-sensitive leaves of induced and vegetative cocklebur plants were made. Fifteen or more protein bands could be separated by polyacrylamide gel electrophoresis when polyvinylpyrrolidone was used in the extracting buffer to remove phenolics. As contrasted to results of others with Pharbilis nil, no differences in stained banding patterns could be detected in vegetative and induced plants. Radioactive leucine, lysine and phenylalanine were incorporated into similar leaf proteins during the last half of an inductive dark period. These experiments and dual-labeling studies with 3H- and 14C-phenylalanine indicated no consistent differences in the types of extracted proteins synthesized by leaves of vegetative and induced plants.