DESIGN: Patients with AIDS-KS who are receiving ritonavir will be administered BAY 43-9006. An initial group of patients will be administered 200 mg BAY 43-9006 once daily, and subsequent groups will receive 200 mg twice daily and 400 mg twice daily respectively. Also two groups of patients with KS and not on ritonavir will be administered 200 mg and 400 mg BAY 43-9006 twice daily respectively. Patients will be studied for toxicity, pharmacokinetics, KS response, the effect on biological markers such as target receptor kinase phosphorylation and signaling molecules in KS tissue. Other parameters that will be assessed will include VEGF levels, the viral load of KSHV, and KS lesion blood flow by non-invasive techniques. If patients tolerate BAY 43-9006, they will receive it for up to 24 weeks. If they have evidence of stable KS or a tumor response, they may receive the drug for up to 54 weeks total.