As reported in previous papers, protease inhibitors such as leupeptin, antipain, chymostatin, pepstatin and phosphoramidon have been obtained from cultured broth of actinomycetes. Elastase (EC 3.4.4.7) reacts with elastin in the elastic tissue and hydrolyzes the peptide bonds involving the carbonyl groups of amino acids bearing uncharged nonaromatic side chains, such as alanine. In this communication, isolation of elastatinal which inhibits elastase is reported. Elastatinal was found in culture filtrates of various species of actinomycetes, one of which (strain MD469-CG8) was used for detailed production and isolation studies. Strain MD469-CG8 was isolated from a soil sample collected in Kumamoto Prefecture and found to be closely related to Streptomyces griseoruber. Antielastase activity was quantified using a modified method of Naughton et al. Elastatinal was produced by shaking culture or tank fermentation of strain MD469-CG8 in media containing carbon and nitrogen sources (e.g., glucose, soybean meal), with maximum production attained after 48-66 hours (rotary shaking) or 38-48 hours (tank fermentation). Purification involved adsorption on active carbon, elution with acetone, Dowex 1x2 column treatment, and SP-Sephadex C-25 chromatography, yielding purified elastatinal with 50% inhibition of elastase at 1.8 μg/ml. Physicochemical properties included melting point 196-204°C (dec), [α]D²⁵ +2° (c1.0, H2O), spectral features, elemental composition (calcd. for C21H36N8O7·2H2O: C45.97, H7.34, N20.42; found: C45.94, H7.13, N19.92), solubility (soluble in water, methanol; insoluble in hexane, benzene), chemical reactions (positive Rydon-Smith, Folin; negative ninhydrin), TLC Rf values, electrophoretic behavior, and pKa values (3.7, >10.5). Amino acid analysis revealed glutamic acid, leucine, and an unusual basic amino acid. Elastatinal specifically inhibited elastase (ID50 1.8 μg/ml) with no significant inhibition of other proteases (trypsin, plasmin, papain, chymotrypsin, thermolysin, pepsin; ID50 >250 μg/ml). It showed no antibacterial/antifungal activity and low toxicity (250 mg/kg intravenous injection in mice caused no death).