In order to study the possible relationship between antigenic phenotype and tumor progression, 63 small cell lung carcinomas (SCLC) biopsies derived from primary or metastatic tumors were tested by immunofluorescence and immunoperoxidase techniques with an anti-carcinoma monoclonal antibody designated MBr1. Primary tumors were found to be less reactive with MBr1 than the local and distant metastatic lesions (57% versus 75% and 89% positivity respectively). A life table analysis on the tested cases indicated an inverse association between the expression of the marker recognized by the MBr1 MAb (CaMBr1) and overall survival (p less than 0.01): patients with MBr1-positive tumors showed a shorter survival time in comparison to patients whose tumors did not express the marker. The same correlation between survival and CaMBr1 expression was found even when only the 31 cases of early stage disease patients were considered (p less than 0.05). Different tumor aggressiveness or resistance to therapy of MBr1-positive tumors could be responsible for the shorter survival time of the patients.