We previously reported isochromophilones I and II from Penicillium sp. as the first microbial-origin inhibitors against gpl20-CD4 binding. Now, we report two additional inhibitors, chloropeptins I (1) and II (2), produced by a soil actinomycete Streptomyces sp. WK-3419. Compound 1 is a new compound, while 2 was identified as complestatin (known to inhibit hemolysis of erythrocytes sensitized by the complement system). This communication deals with their fermentation, isolation, characterization, and biological activities. The inhibitory activities against gpl20-CD4 binding were monitored by ELISA. A seed culture of Streptomyces sp. WK-3419 was prepared, and then transferred to a 50-liter jar fermentor for production. The mycelium cake from the cultured broth was extracted with 70% aqueous acetone, followed by solvent extraction (ethyl acetate at pH 2), silica gel column chromatography, and HPLC (Shiseido Capcell pak C18-SG column) to obtain 1 (111 mg, yellow powder) and 2 (67 mg, yellow powder). The physicochemical properties of 1 were as follows: mp >300°C; [α]₂₆⁰ -18.7° (c=0.16, DMSO); UV λₙₘ (ε): 214 (64,600), 239(sh), 285(sh), 291(14,600), and 304(sh); molecular formula C₆₁H₄₅N₇O₁₅Cl₆ (determined by HRFAB-MS). The structure of 1 was determined by comparison with 2 (complestatin) via NMR: three aromatic proton signals of 1's indole moiety indicated that C-7 of the indole ring is conjugated to an adjacent phenol group, so 1 was named chloropeptin I. Compounds 1 and 2 inhibited gpl20-CD4 binding with IC₅₀ values of 2.0 μM and 3.3 μM, respectively. They showed no antimicrobial activity against various bacteria and fungi at 1.0 mg/ml, and no cytotoxicity against B-16 melanoma at 20 μM. Compound 1 significantly inhibited HIV replication in peripheral human lymphocytes at 7.5 μM without affecting cell proliferation. Both 1 and 2 were found to inhibit the binding between gpl20 and CD4 and exhibit selective anti-HIV activities, which may block HIV entry into lymphocytes (complestatin (2) was previously reported to inhibit HIV-1-induced cytopathicity and syncytium formation in CD4+ T-lymphocytes). The structure elucidation of 1 will be reported elsewhere.