Polypeptides phosphorylated in vivo in Drosophila mutants defective in learning and memory, were characterized by polyacrylamide gel electrophoresis of subcellular fractions obtained by phase partitioning in Triton X-114 [3]. In the mutants turnip, dunce and Shaker, one or more bands at a molecular weight range of 50-80 kDa had altered 32P incorporation. Some of these bands were altered in more than one mutant. In the mutant rutabaga no significant differences from wild-type were observed. The data suggest that phosphoproteins that could be potentially related to learning mechanisms might be identified in some learning mutants.