Immobilisation of cells in a calcium alginate gel improved plasmid stability (up to 50%) and enzymatic expression (up to 57%) of a recombinant Saccharomyces cerevisiae over-expressing the homologous gene EXG1. The rate of segregational loss in the free cells was 14-fold higher than that of the immobilised cells. Recombinant protein synthesis requires reduced cofactors, which affect the redox balance of the cell.