Human alpha(1)-antitrypsin (alpha(1)-AT) was expressed and secreted in Saccharomyces cerevisiae carrying the gal1 and reg1-501 mutations under the control of GAL10 promoter. Increasing galactose from 0 to 0.5 g/l increased the extracellular concentration of alpha(1)-AT, though the secretion efficiency was decreased. The final titre of alpha(1)-AT secreted and the secretion efficiency were 17.9 mu g/ml and 24.8%, respectively, with 0.5 g galactose/l.