Two types of light chains were observed in clathrins from different bovine tissues. Clathrin was purified from seven different bovine tissues using immunoaffinity columns prepared from a monoclonal antibody specific for the heavier light chain (LCa) of bovine brain clathrin. The LCa equivalent in clathrin from non-brain tissue was identified by monoclonal antibody binding to electrophoretic blots of these clathrins. The LCa and LCb light chains of bovine brain clathrin are, respectively, 4 X 10(3) daltons and 3 X 10(3) daltons heavier than their corresponding light chains in other tissues. The light chains from tissues other than brain are similar in molecular weight.