A rapid immunohistologic method is described to analyze the possible cell origin of a given neoplasm during surgery by using selected examples of monoclonal and polyclonal antibodies (anti-cytokeratins, anti-vimentin, anti-leukocyte common antigen, and anti-keratin). This rapid (26-28 min) procedure, consisting of a two-step immunoperoxidase method, did not differ in terms of intensity and specificity of the immunoreaction from the control procedure for which conventional longer times of incubation and washing were used. The results demonstrate the feasibility and effectiveness of the procedure.