Clonal subpopulations of neoplastic cells were derived, in soft agar, from the spontaneously metastazing variant (MV522) of a human lung carcinoma cell line. The ability of these clones to spontaneously metastasize from subcutaneous sites in athymic mice was then tested. A variation in metastatic ability was expected with the derivation of some low metastatic clones and some high metastatic ones. However, all of the derived clones, although equally tumorigenic, were less metastatic than the parental variant. These clonal cell lines can now be used in a systematic analysis of events associated with the reversion to a less malignant state.