Bone metastases reproducibly developed in nude rats after an injection of LOX human malignant melanoma cells into the left ventricle, with hind leg paralyses appearing in all animals within approximately 2 weeks. Manifest metastases were present exclusively in the skeletal system, predominantly in the lumbar portion of the spine, the long bones, and occasionally in the skull. Intracardially injected 125I-labeled tumor cells and monodisperse microspheres were distributed in parallel to the various tissues. Moreover, because the levels of radioactivity were significantly lower in bone than in lung, kidney, and liver, the pattern of metastases could not be explained solely by hemodynamic factors. In chemotherapy experiments, the survival time of rats given left ventricular injections of LOX cells increased in a dose-dependent manner after the animals were treated with dacarbazine. Researchers may find the model useful for studying the biology of bone metastases and for testing the sensitivity of these lesions to drugs.