Using two direct introduction methods, DNA synthesis or cell proliferation activities of three purified proteins from E. coli, namely, human papillomavirus (HPV) E7 proteins of type 16, a mutant type 16 (24 C-G) (transformation defective) and type 6b, were measured in mouse fibroblast, C127 cells. By a microinjection method, the order of the cell mitotic indexes for the three E 7 proteins as determined by 5-bromo-2'-deoxy-uridine (BrdU) staining was type 16, 6b and 16 (24 C-G). By the osmotic shock method, the ³H-TdR incorporation and coloration by (3-carboxymethoxy phenyl)-2-(4-sulfophenyl)-2H-tetolazorium (MTS) for the three proteins correlated with the pRb binding and focus forming activities previously reported (hunger et al. 1991). These results indicate that the simple osmotic shock method for direct protein introduction may be generally useful for transformation assays of oncoproteins.