Apart from modulation of tumor-cell drug sensitivity, induction of differentiation might be an alternative in the treatment of tumors resistant to cytotoxic drugs. In this report the capacity to induce differentiation and to modulate the cis-diamminedichloroplatinum(II) (CDDP) sensitivity of all-trans-retinoic acid (RA), docosahexaenoic acid (DCHA), and hexadecylphosphocholine (HePC) is examined in human germ-cell tumor cell lines. In the embryonal carcinoma cell line Tera-2 and its 3.7-fold CDDP-resistant subline Tera2-CP, we evaluated the effects of 96 h of pretreatment with RA (0.1 μM ), DCHA (23 μM ), and HePC (25 μM ) on differenctiation induction and on CDDP-induced cytotoxicity, DNA platination (4-h incubation), and apoptosis (continuous incubation). Without drug treatment, Tera2-CP showed less apoptosis than Tera-2. Pretreatment with RA decreased the cytotoxicity and apoptosis induced by CDDP without resulting in decreased DNA platination and increased differentiation in both cell lines. DCHA enhanced CDDP-induced cytotoxicity and apoptosis and did not affect the embryonal character of either cell line. HePC did not affect CDDP cytotoxicity or differentiation in either cell lines. Effects of the modulators on differentiation and on CDDP-induced cytotoxicity, DNA platination, and apoptosis did not differ between Tera-2 and Tera2-CP. RA can be applied for differentiation induction in CDDP-resistant germ-cell tumor models. However, in this model, RA reduced the apoptotic susceptibility. DCHA potentiated CDDP cytotoxicity in vitro; its in vivo modulatory capacity in germ-cell tumor cells deserves further study.