Hybridomas secreting monoclonal antibodies specific for human lung cancer were produced by fusing immunized mouse spleen cells with mouse myeloma line X63-Ag8.653. Prior to fusion, BALB/c mice were immunized with two different histological types of human lung cancer (Squamous cell carcinoma and adenocarcinoma) obtained from surgery. An immunocytoadherence test was used to select hybridomas secreting antibodies that bound the patient's lung tumor, but did not bind to a B-lymphoblastoid cell line derived from the same patient. Five stable antibody-producing hybrids have been established and cloned. The antibodies produced by these clones have been characterized according to their light and heavy chain isotypes and for their specificity. In addition to binding to the tumor used for immunization, the antibodies bound to other lung tumors of the same histological type (i.e., squamous cell or adenocarcinoma). This reactivity was observed with both established lung tumor cell lines and with fresh tumors obtained from biopsy of patients in our clinic. Some significant reactivity was also observed with large cell carcinoma but the antibodies did not react with small cell carcinomas of the lung, bronchiolo-alveolar cell carcinoma, cancer of the esophagus and stomach, melanomas, several types of leukemias, normal human lung tissue, fibroblasts, or erythrocytes of type A, B, or O. Two of the five antibodies, 5C7 and 5E8 cross-reacted with one breast cancer obtained from surgery, and 5C7 also cross-reacted with one melanoma biopsy specimen. These results suggest that we have generated monoclonal antibodies that recognize a set of antigenic determinants that are commonly expressed on a portion of human lung tumors that are not detectable on a variety of other human tumors or normal human tissue.