Abstract Activated spleen T cells are invasive in hepatocyte and fibroblast cultures, and this property is dominantly expressed in T cell hybridomas. The invasive potential of the hybrids correlates with their capacity to disseminate in vivo. We have used this model to study the invasive and migratory properties of cytotoxic T lymphocytes (CTLs). TWo murine CTL clones were highly invasive, independent of their state of activation. CTL hybridomas, derived from one of the clones, were similarly invasive. In vivo, CTL hybridoma cells disseminated to extravascular sites in the liver, kidneys, lungs, ovaria, tubae, uterus, and lymphoid, mesenchymal, and fat tissues. Within 7 to 14 days, 106 cells were lethal in 100% of mice. The adhesion molecules CD2, CD8, CD54, L-selectin, and CD49d (VLA-4 and LPAM-1 α-chain) were not expressed by all CTL hybridomas and therefore not indispensable for invasion in vitro and dissemination in vivo. In contrast, LFA-1 (CDlla/CD18), CD44, and VLA-6 (CD49f/CD29) were expressed on all hybrids. LFA-1 antibodies inhibited CTL hybridoma invasion in vitro, but antibodies inhibiting CD44-hyaluronate and VLA-6-laminin interaction had no effect. These results suggest that migration of cytotoxic T cells into non- inflamed tissues is independent of their activation state and does not require L-selectin, LPAM-1, CD2, and VLA-4. J. Leukoc. Biol. 53: 381–389; 1993.