An important tool for studying the regulation of synapses is a rapid and reliable means of separating synaptic and intracellular proteins. This unit presents a technique for analysis of brain tissue which relies on differential centrifugation to separate proteins present at synaptic sites from those found in intracellular cytoplasmic and vesicular pools. The method is efficient in that only small amounts of tissue, such as might be obtained from a small region of a rodent brain, are required. It is reproducible and, in conjunction with immunoblot or immunoprecipitation techniques, can produce reliable quantitative data. The protocol will be of interest to those conducting a variety of different studies related to the localization and trafficking of brain receptors and signaling molecules.