A method is disclosed for increasing the efficiency of retroviral mediated gene transfer into viable target cells, which comprises transducing the target cells by infecting the target cells with a replication defective recombinant retrovirus that infects the target cells in an aqueous medium in the presence of (a) a mixture of an effective amount of a first functional material having a retrovirus binding domain that binds said retrovirus, and an effective amount of a second functional material having a target cell binding domain that binds said target cell, or (b) an effective amount of a bifunctional material having both a retroviral binding domain which does not contain the heparin binding domain derived from human fibronectin, and a target cell binding domain, wherein the bifunctional material has a retrovirus binding domain that binds to said retrovirus and a target cell binding domain that binds to the target cell.