One of the factors required for successful retroviral transduction is contact between viral particles and target cells. We hypothesized that combining agents that improve virus-target cell interaction via different mechanisms will increase transduction efficiency. We examined the transduction efficiency of leukemic K562 cells, primary normal and chronic myelogenous leukemia CD34+ cells with the amphotropic retroviral vector, G1Na, packaged in PA317 by enumerating G418-resistant colonies in semisolid media. We evaluated the ability of the recombinant fibronectin fragment, CH296, cationic lipids, or a transwell flow-through system, alone or in combination to improve retroviral transduction. Transduction of K562 cells improved 1.5 to two-fold with lipids or CH296, while their combination improved transduction 2.5-fold. Transduction of K562 cells in the transwell flow-through system improved transduction three-fold. Transduction of normal (NL) CD34+ CFC improved 10-fold with lipids and 20-fold with CH296. Lipid and CH296 had synergistic effects. The transwell flow-through system improved transduction of normal CD34+ CFC 30-fold. Finally, similar to what was seen for K562 cells, transduction of CML CFC improved two- to three-fold with either CH296 or lipids, whereas the combination had synergistic effects. We conclude that any physical means that enhances contact between viral particles and target cells improves transduction. Two such methods that have different action mechanisms have additive or synergistic effects on transduction.