The vector pE1 is derived from the plasmid pKD1 isolated from the yeast Kluyveromyces lactis. It can be maintained stably in the yeast K. lactis at high copy number. We explored the possibility of using the pKD1/K. lactis system for heterologous gene expression. The human interferon alpha A secretion cassette was inserted into pE1. The obtained plasmid, pE-IFN1, showed slightly instability when compared to pE1. The data showed that the secretion signal sequence of the alpha factor of Saccharomyces cerevisiae was functionally active in K. lactis. The K. lactis transformants carrying pE-IFN1 secreted efficiently IFN into the growth medium when they were grown in nonselective medium. The total amount of IFN released reached 1-2 mg per liter of culture supernatant.