Immunoenzymatic labeling is not currently used in the frozen-section diagnosis of tumors, in view of the length of the procedure. The authors tested whether, without loss of specificity and sensitivity, the labeled avidin-biotin (LAB) method may be adequately shortened for use in frozen-section diagnosis. Cryostat sections of tumors of various types and different degrees of differentiation and a panel of monoclonal antibodies to various molecular weight cytokeratins, vimentin, and leukocyte common antigen was used. The entire LAB procedure was completed in less than 7 minutes. For comparison, all tumors were also stained by the conventional avidin-biotin complex (ABC) method, which required more than one and a half hours for completion. The pattern and intensity of specific staining for the two procedures was identical, and the background staining was minimal with the LAB method. In view of the short time required to obtain specific staining, the quick LAB method may be of great value for characterization of primary or metastatic tumors in frozen-section diagnosis.