The technique efficient for hybridization of mammalian cells was improved by combining a procedure of cell agglutination of cells pretreated with a combination of lectin and polycation and the procedure of conventional polyethylene glycol (PEG) -induced cell fusion. The agglutinability of cells treated with lectin, polycation, and both of them was tested. The effects of these agglutinogens on the hybridization frequencies of cells were also compared. The appearance rate of hybrid colonies was found to be correlated to the extent of cell agglutination. The pretreatment with a combination of lectin and polycation induced the highest degree of cell agglutination and the highest frequency of resulting hybridization. The enhancing effect by the pretreatment with a combination of these agglutinogens on the hybridization frequency was confirmed through experiments on the crosses of several cell types including nuclear fraction (karyoplast).