There are yet no human studies reported on Doxil pharmacokinetics when combined with MDR modulators. Preclinical data shows that pharmacokinetics of Doxil, unlike free doxorubicin, is minimally affected by the addition of PSC 833 (36). Enhanced tumor toxicity was observed when PSC 833 was combined with Doxil. Since doxorubicin, the active agent in Doxil, is metabolized by the same cytochrome P450, interactions between these 2 agents may have very significant clinical implications. The purpose of this study is to assess the toxicity and determine the maximum tolerated dose of Doxil when combined with PSC 833 in the treatment of AIDS-KS and other advanced malignancies.