Trichosanthin was purified from fresh Chinese root tubers ofTrichosanthes kirilowiiand evaluated for anti-HIV activity. Trichosanthin inhibited syncytium formation between infected H9 cells and uninfected Sup-T1 cells from 0.5 to 4 μg/ml. Trichosanthin also inhibited HIV replication in H9 and CEM-SS cells at 1 μg/ml, but was toxic for MT-4 cells (HTLV-1-positive), at doses greater than 0.25 μg/ml. This new purification procedure confirms the anti-HIV activity of trichosanthin on some cell lines in different biological assays.