Using subrenal capsule implantation (SRC) in nude mice we have isolated 4 new sublines (RC43MSP, MBO, MLI, MDI) from the human renal cell carcinoma line (HRCC) RC43. These sublines exhibit an enhanced metastatic ability and a faster doubling time after subcutaneous (SC) transplantation in vivo, when compared to the parental line. With the aim of a better characterization of these new sublines we have performed a flow cytometric analysis (FA) of the DNA content and studied the motility response (MR) to laminin and fibronectin. FA results. The RC43 parental line showed a tetraploid pattern (DNA index: 2.08). Also the variant lines RC43MLI and RC43MDI were tetraploid (DNAind: 2.05 and 2.07, respectively). With RC43MDI a second peak in the tetraploid range was evident. The RC43MSP and the RC43MBO sublines both showed a hypertetraploid pattern (DNAind respectively 2.21 and 2.11). MR results. Motility studies showed that all RC43 lines, including the parental line, were stimulated to migrate in response to either laminin or fibronectin both from rat and human sources. There were no significant differences between the parental line and its variants in this respect, however. We conclude that by the use of FA at least two of the sublines (MSP and MBO) can be distinguished from the parental RC43 cell line, suggesting a different clonal origin of the various sublines. As all sublines, as well as the parental line, showed a large but similar response to migration-stimulating agents (such as laminin and fibronectin) determination of MR could not be used to obtain a further discrimination between the different sublines.