We have prepared cat forebrain synaptosomes in order to investigate the presence of actin-like proteins. First, actin-like filaments were demonstrated using a heavy meromyosin binding technique. Decorated filaments form networks inside the synaptosomes and are frequently seen in relation to membranes and synaptic vesicles. Second, using SDS-polyacrylamide gel electrophoresis, a band corresponding to actin appears to be one of the major constituents of synaptosomal fractions; this confirms the work of Fine and his coworkers. The significance of actin-like filaments in relation to axoplasmic transport is briefly discussed.