A thermostable extracellular glucoamylase from Thermomyces lanuginosus in static culture was purified to SDS–PAGE homogeneity by fractional ammonium sulphate precipitation, ion-exchange chromatography on DEAE–Toyopearl, Butyl–Toyopearl hydrophobic interaction chromatography, gel filtration on Sephacryl S-300 and ion-exchange chromatography on FPLC MonoQ. The molecular weight of the enzyme, consisting of a single polypeptide, was estimated to be 72000 by SDS–PAGE. The glucoamylase exhibited maximal activities at pH 5·0. The optimum temperature for the activity was 70°C. The enzyme was thermostable at 60° with half-lives at 70° of 20 min and 80° of about 6 min. The glucoamylase was a glycoprotein with 11·4% carbohydrate content. The enzyme hydrolysed soluble starch, amylose, amylopectin, dextrin, glycogen, maltotroise and maltose. Starch was the best substrate.