The question of whether metastatic potential and drug resistance are related phenotypes was addressed by comparing the biological behavior of the parental B16 melanoma and a multidrug resistant variant derived from it, the B16/Col/R. A more pronounced metastatic spread to lungs was observed in mice inoculated i.v. with the B16/Col/R variant than in those bearing the parental line. In addition, in the mice injected with the drug resistant melanoma, unusual tumor masses were observed. Large abdominal and spinal cord growths were seen with the MDR variant but not encountered in mice inoculated with the original B16 melanoma. We further attempted to test the capacity of the two cell types to perform several cellular functions relevant to the metastatic process. The B16/Col/R cells displayed a higher aggregability and cell motility than did the B16 cells. Adherence to endothelial cells was higher in the parental line than in the B16/Col/R, possibly supporting a more efficient extravasation of the variant cells. The drug resistant variant displayed a higher capacity to grow locally in kidney, spleen, cecum and peritoneum, as compared to the parental melanoma, indicating a higher ability of homing and growth in these potential target organs for metastasis. A correlation between metastatic potential and multidrug resistance appears therefore to exist in the system examined.