The human nucleolar antigen p120 was detected with an anti-p120 monoclonal antibody (MAbp120) in most human malignant tumors (Freeman et al., Cancer Research, 48, 1244-1251, 1988). Stable transfection of the sense p120 cDNA caused malignant transformation of NIH/3T3 cells in vitro, and the antisense p120 constructs markedly delayed the growth of these transformed cells (Perlaky et al., Cancer Research, 52, 428-436, 1992). Several p120 antisense phosphorothioate oligonucleotides designed to hybridize with different regions of the p120 sequence were screened on human tumor cell lines in vitro. Marked growth inhibition of HeLa, LOX and HRCC cell lines was found, particularly with antisense p120 oligonucleotide ISIS 3466 in combination with N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA); oligonucleotide ISIS 3466 is complementary to a non-translated region at the 3' end of the molecule. Preliminary in vivo studies on human LOX ascites tumor in nude mice showed marked inhibitory effects on tumor growth by the antisense oligonucleotide ISIS 3466 in the presence of DOTMA when treated on alternate days.