By somatic cell fusion studies between noninvasive mouse T-lymphoma cells and invasive human activated normal T-cells we have previously shown that the genetic information responsible for the induction of invasive and metastatic potential in interspecies T-cell hybrids is located on human chromosome 7. Apparently, genes derived from normal activated T-cells are dominantly expressed in the hybrids and control the invasive and, as a consequence, metastatic potential of these T-lymphoma cells. To sublocalize the invasion-inducing locus on chromosome 7 we have generated hybrids that harbor only specific regions of human chromosome 7 with or without a small fragment of human chromosome 21. Analysis of these hybrids revealed that the invasion-inducing locus maps to 7p12→cen. The human DNA complement of the hybrids was confirmed by Southern blot analysis using a large panel of chromosome 7-specific DNA probes. Several of these genes could be further sublocalized. These included: ARAF2 to 7p12→cen, D7S21 to 7pter→p12, ACTB to 7p15→p12, EGFR to 7p12, MDH2 to 7cen→q22, and PDGFA to