The protein and allergen contents of four commercial soybean skin test extracts were tested by SDS-PAGE and immunoblotting using sera from soy-allergic adults. Polyacrylamide gels stained with Coomassie Blue showed an absence of several major soybean proteins, particularly those at higher molecular weights. The acidic subunits of glycinin and beta-conglycinin, major soybean storage proteins, appear to be absent or present in much reduced amounts. Immunoblots with soy-allergic sera indicate alteration, reduction, or loss of IgE-binding in the commercial extracts as compared to extracts of soy flour. In one soy-allergic patient, skin tests revealed a negative response to three of the commercial soybean extracts and a mild response to one extract. Defatted soy flour obtained from two of the four extract manufacturers was extracted in the laboratory using a standard procedure for the isolation of soybean proteins. In one case, the extract still had an abnormal protein profile on gel electrophoresis while in the other case, the new extraction procedure gave significantly improved extraction of soy protein. Preparation methods appear to be partially responsible for the variable allergen content in commercial soybean skin test extracts.