We have established two highly metastatic tumor clones, D-1 and F-3, which have the distinct features of undergoing pulmonary metastases. Both clones were derived from a skin squamous cell carcinoma (SqC-NH), which had spontaneously occurred in DS-Nh mice. F-3 was morphologically spindle-shaped in tumor mass and adherent in culture, while D-1 was round and non-adherent. In in vitro growth, there was no significant difference between them. When the clonal tumor cells were implanted intradermally into syngeneic mice, however, the growth of D-1 was slower than that of F-3. As for the metastatic ability, both D-1 and F-3 were highly metastatic compared with the original tumor. Interestingly, the pulmonary metastases of these two clones were apparently different. In F-3-bearing mice, some round nodules were detected and no tumor cells were seen in the surrounding area around the nodules (nodule-type). In contrast, D-1 cells had initially grown from the periphery of lobes, and interstitially infiltrated the lung parenchyma area without forming nodules (diffuse-type) and the appearance was similar to lymphagitis carcinomatosa. Histologically, a remarkably smaller number of metastatic foci formed around the blood vessel for D-1 as compared with F-3. It should also be noted that some localized nodules (nodule-type both visually and histologically) were seen in the lung, when D-1 cells were inoculated in the tail vein. In addition, D-1 showed markedly higher lymphatic metastasis than F-3. These observations show that the pulmonary metastases of D-1 and F-3 differ in the mechanisms underlying the processes of tumor dissemination. We suppose a possibility that D-1 may preferentially metastasize via the lymphatics and F-3 may metastasize via the bloodstream.