Maltose tetrapalmitate (MTP), a non-toxic synthetic glycolipid analog of lipid A, has been shown to have antitumor activity in tumor-transplanted animals. Its mode of action has been postulated to be as an immunoadjuvant or as an anti-angiogenesis agent. MTP has been shown to have antitumor properties in lung, bladder, mammary, colon, liver and soft tissue tumors, but its action on prostate cancer has not yet been investigated. The effect of MTP alone and in combination with hydrocortisone hemisuccinate on prostate cancer and the ability of MTP to inhibit angiogenesis were examined in this study. In vitro, MTP was minimally cytotoxic to rat prostate cancer cells and to bovine and human endothelial cells at high concentrations. In the angiogenesis inhibition assays, the MTP alone exhibited no anti-angiogenesis effect and significant anti-angiogenesis activity only when combined with hydrocortisone hemisuccinate at high doses. In vivo, however, MTP demonstrated significant inhibition of prostate cancer growth. These results suggest that MTP decreases prostate cancer growth in vivo but it is not an angiogenesis inhibitor in rat prostate cancer.