Specific precipitates and purified human antibodies were reduced and alkylated and subjected to starch gel electrophoresis in 8 M urea to dissociate and separate the L and H polypeptide chains. Dissociated antibodies to dextran, levan, teichoic acid, blood group A substance, and tetanus toxoid showed sharp bands corresponding to L polypeptide chains. The patterns differed for antibodies of different specificities. Some differences were also seen among antibodies of the same specificity from different individuals. Purified antidextran antibodies showed particularly simple patterns resembling those of purified human gamma myeloma proteins. In some cases only one L chain band was present.