ABT-510 is an angiogenesis inhibitor derived from thrombospondin-1, a naturally occurring inhibitor of angiogenesis. We investigated ABT-510, which was administered subcutaneously in patients with advanced solid malignancies, to assess safety, pharmacokinetics, and serum markers of angiogenesis. ABT-510 was administered subcutaneously as a continuous infusion (100 mg/24 h) and bolus injections (100, 200, and 260 mg once daily; 50 and 100 mg twice daily) in 28-day cycles. Thirty-nine patients received a total of 144 treatment cycles. Administration by continuous infusion was hampered by the onset of painful skin infiltrates at the injection site. In the bolus injection regimens, the most common toxicities observed were mild injection-site reactions and fatigue. Maximum-tolerated dose was not defined, but 260 mg was defined as the maximum clinically practical dose. ABT-510 pharmacokinetics were linear across the dosage ranges tested, and the potential therapeutic threshold (plasma concentrations > 100 ng/mL > 3 h/d) was achieved with all dose regimens. Median serum basic fibroblast growth factor (bFGF) levels decreased from 14.1 pg/mL (range, 0.5 to 77.7 pg/mL) at baseline to 3.2 pg/mL (range, 0.2 to 29.4 pg/mL) after 56 days of treatment (P = .003). No correlations with time on study or ABT-510 dose or exposure were observed for individual changes in bFGF. Stable disease lasting for six cycles or more was seen in six patients. ABT-510 demonstrated a favorable toxicity profile and linear and time-independent pharmacokinetics with biologically relevant plasma concentrations. The significant number of patients with prolonged stable disease and the convenient method of dosing merit further studies with this angiogenesis inhibitor.