The present invention relates to the use of a glucosidase II mutation to increase protein secretion in eukaryotic cells. The present invention relates further to the use of eukaryotic cells, comprising a mutant glucosidase II gene, possibly in combination with the expression of a recombinant .alpha.-1,2-mannosidase gene and/or a recombinant N-acetylglucosaminyl-transferase gene, as a host for protein secretion.