Green malt contains a number of peptidases, called metallopeptidases, that are inhibited by metal-chelating agents, and it was reported recently that metallopeptidases inhibited by 1, 10-phenanthroline contributed to the protein solubilization that occurs during mashing. However, this group of germinated barley enzymes has received little attention; none of them have been isolated previously and their functions in green malt have never been studied. We have now isolated a group of five metallopeptidases from green malt that was prepared from the six-rowed malting barley (Morex), using anion exchange chromatography and chromatofocusing. The enzymes were studied using one- and two-dimensional polyacrylamide gel separation systems with gels that contained incorporated gelatin substrate. The enzymes were all inhibited by the metal chelating agents 1,10-phenanthroline and EDTA, indicating that they were metallopeptidases. Like metallopeptidases from other sources, their activities were also impaired by the reducing agents cysteine, 2-mercaptoethanol and dithiothreitol. The EDTA-inactivated peptidases were reactivated by the presence of low concentration of certain metal ions. However, in the presence of more concentrated metal ions, especially zinc, the peptidase activities were again decreased. The metallopeptidases hydrolyzed gelatin fastest at pH 8.0. All five of the enzymes shared these biochemical characteristics and had similar acidic pI values and gel mobilities, suggesting that they were probably isoforms. When a preparation of hordeins (barley storage proteins) was used as substrate for the metallopeptidase preparation, the D hordein component was readily hydrolyzed. This, together with the stability of these enzymes during kilning and the aforementioned effect of 1, 10-phenanthroline on protein solubilization during mashing, indicates that these enzymes might play a role in degrading storage proteins during malting and mashing. Moreover, the finding that metal ions and reducing agents strongly affect the metallopeptidase activities suggest that it might be possible to control their activities during brewing and thus vary wort soluble protein levels.