The antitumor activity of 5-fluoro-2'-deoxyuridne (FUdR) against P388 leukemia was markedly enhanced by addition of guanosine-5'-monophosphate (GMP). With daily i.p. treatment for 5 d, the combination of FUdR at 100 mg/kg/d and GMP at 30O mg/kg/d showed the highest antitumor effect (more than 290% ILS), while maximum ILS of FUdR alone (100 mg/kg/d) was 94%.
