A methylcholanthrene-induced fibrosarcoma (3AM) and several of its clones were evaluated for pulmonary metastasis, growth rate, and chromosome composition. Heterogeneity was observed in the three parameters, and no correlation was found between growth rate and metastatic potential. Furthermore, three clones (10, 34, and 27) were identified with distinctive, high or low, metastatic potential and marker chromosomes. The marker chromosomes characteristic for each clone were identified in the early passages of the parental 3AM line, indicating the preexistence of the different cell types in the original neoplasm. The three clones were then characterized as to tendency to adhere to vascular endothelium, immunogenicity, and antigenic specificity. Clone 10, with two large metacentric markers (T2, 4 and T10, 15) and the highest metastatic potential (221 foci/lung), expressed the highest endothelial attachment and immunogenicity. Clone 27 was characterized with an extremely low rate of metastasis (nine foci/lung) and a T2, 7 large acrocentric marker, while clone 34 was characterized with a moderate rate of metastasis (107.5 foci/lung) and a T4, 16 acrocentric marker. Antigenically, clone 10 cross-reacted with clones 34 and 27 and 3AM, while clones 27 and 34 cross-reacted with clone 10 and 3AM but not with each other, suggesting that, within the original tumor, there were common tumor antigens shared by some cells but no universal antigen shared by all cells.