Monkey Clara cell 10 kDa protein (CC10) was purified from monkey lung lavage. This protein showed an apparent molecular weight of about 10 kDa and 5 kDa under non-reducing and reducing conditions, respectively, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. From the amino acid sequence data, monkey CC10 protein consisted of two identical 70-amino-acid polypeptide chains joined by two cystine residues, and possessed sequence identities of 78.6%, 52.9%, 52.9%, and 44.3% with human CC10, rat CC10 (PCB binding protein), rabbit uteroglobin, and mouse CC10, respectively. When monkey CC10 was compared with rabbit uteroglobin (progesterone binding protein), two polar residues of Tyr-21 and Thr-60, important for progesterone binding specificity, were substituted for Phe-21 and Met-60, and thus monkey CC10 may not have a binding capacity with progesterone. Monkey CC10 also possessed a surface homology with lipocortin I (anti-inflammatory peptide), thus suggesting that monkey CC10 plays a role in the anti-inflammatory process at the air-liquid interface over the bronchio-bronchiolar epithelium.