Antitumor marine coral prostanoids (clavulone II and chlorovulone I) were entrapped into lipid microspheres of 0.2 micron diameter to make lipo-drugs. Daily treatment with lipo-chlorovulone I (1.6 mg/kg/day, i.p.) and lipo-clavulone II (12.5 mg/kg/day, i.p.) on days 1 through 5 markedly prolonged the survival time (135% ILS and 73% ILS, respectively) of mice inoculated with sarcoma 180 as compared with that of a corresponding dose of respective free chlorovulone I and clavulone II. These results suggest that lipid microspheres may be used as drug delivery carriers for antitumor coral prostanoids in vivo.