In order to study the relationship between tumor transplantability to the nude mouse and abnormality of the myc family genes (c-myc, N-myc, L-myc) in human primary lung cancers, 32 various lung cancers were analyzed for abnormality of the myc family genes by Southern blot hybridization, and were transplanted s.c. into nude mice. Southern blot analysis showed that four non-small cell carcinomas and three small cell carcinomas had amplified c-myc and L-myc genes, respectively. Allelic deletion of the L-myc gene was observed in seven cancers, of which two also had an additional band of the c-myc gene or amplification of the L-myc gene. No abnormality of the N-myc gene was observed in this series. Of 13 cancers with abnormality of the myc family genes, 11, including all tumors with myc gene amplification, were transplantable to nude mice. Of 19 tumors without any abnormalities of the myc family genes, however, only five were transplantable to nude mice (P less than 0.005). These results indicate that abnormality of the myc family genes, especially gene amplification, might promote tumorigenic ability in xenotransplantation of lung cancers and this phenomenon might be closely related to the function of the myc gene.