Total β-amylase (T-β-A) activities in barley and malt were determined by the conventional method with papain and by the newly proposed method with 2-mercaptoethanol containing papain. Comparison between the activities determined by both methods during germination of barley made it clear that the new method was of propriety to determine the true T-β-A activity in barley or malt and that the conventional method was still useful for a prediction of salt-soluble active β-amylase (A-β-A) activity in malting barley after germination. Though the amount of A-β-A in malt produced by normal germination did not reach to that of T-β-A determined by the new method, the gibberellic acid treatment of barley was found to enhance the activation of zymogen β-amylase (Z-β-A) in vivo which resulted in the increase in the papain-soluble A-β-A activity up to that of T-β-A. From these results it is quite possible that all the types of Z-β-A are activated by devices on malting method and that the increase in A-β-A activity during germination is exclusively due to the activation of Z-β-A formed during ripening and dormancy of barley.