Ophiostoma floccosum, an ascomycete, is being developed as a new expression system for the production of foreign proteins. Enzymes for starch degradation and several proteases are amongst the most efficiently secreted proteins of Ophiostoma. The organism secretes only a few proteins into the culture medium, which provides a considerable advantage for the purification of any recombinant gene product. Several mutants of O. floccosum derived by UV mutagenesis have been isolated and the total the amount of secreted protein was increased by 4 to 6 times. The amylase activity of the best mutant was improved 240-fold compared to the parental strain. The proteinase profiles in the culture supernatants of several key mutants have been characterised for the selection of a suitable expression host for a particular gene product. The regulatory sequences and the protein encoding region of α-amylase, one of the dominant secreted proteins, have been isolated. A series of expression vectors containing the α-amylase regulatory sequences and sequences encoding the mature α-amylase enzyme gene have been constructed. The expression system is being tested using dsRed as a reporter gene.