The present invention relates to the general field of recombinant protein expression, purification of recombinant proteins, diagnosis of HCV infection, prophylactic treatment against HCV infection and to the prognosing/monitoring of the clinical efficiency of treatment of an individual with chronic hepatitis, or the prognosing/monitoring of the natural disease. In particular, the present invention relates to the use of yeast, i.e. Hansenula or Saccharomyces glycosylation minus strains, for the efficient expression of HCV envelope proteins that are core-glycosylated, purification methods for these proteins, and the use in various applications, such as the use in diagnosis, prophylaxis or therapy of HCV envelope proteins purified according to the present invention.