Using the modified yeast expression vectors that contained phosphoglycerate kinase or chelatin promoter with the adenine (A) base at -3 position from the ATG coding sequences and the leu-2 gene, recombinant human interleukin-6 (rhIL-6) was produced as a beta-galactosidase (lacZ) fusion protein in Saccharomyces cerevisiae. Expression level of the IL-6-lacZ was 12 times higher than that from the unmodified wild type plasmids and IL-6 activity was 9-9.8 x 10(5) unit/mg yeast total protein. Thus these modified yeast vectors are useful for high expression of foreign genes in yeast.