The expression of the bacterial neomycin resistance (NmR)-encoding gene was examined under control of the promoter region of the gene encoding the human polypeptide chain elongation factor 1 alpha (EF-1 alpha). In a human liver cell line, HepG2, the plasmid pEF321-neo directed higher expression of the bacterial neo gene than the NmR gene expression vectors using other promoters, like the SV40 early region or thymidine kinase of Herpes simplex virus and SV40 early region promoter linked to human T-cell leukemia virus-1 enhancer sequences.