Human calcitonin (hCT) is a 32 amino acid peptide participating in the regulation of calcium and phosphorus metabolism in humans. It is used in clinics for treatment of diseases related to bone decalcification, such as Paget disease, osteoporosis imperfecta, parathyroid gland carcinomas, etc. A synthetic hCT tetrameric (hCT_t) gene is now cloned in binary vectors for gene expression in yeast and plants. The vector for expression in yeast is based on 2μ plasmid containing the α-factor leader sequence. The plasmid for expression in plants carries the 35S cauliflower mosaic virus promoter linked to the tobacco etch virus 5′-nontranslated leader sequence acting as a translational enhancer. Two strains of yeast cells (GRF18 and VY168) and one cultivar of potato (Solanum tuberosum Nevski) were transformed and expression of the hCT_t gene was studied by mRNA-DNA hybridization, RT-PCR, Northern-blot analysis, ELISA and RIA. The yield of recombinant hCT_t was estimated to be about 12–20 mg per liter of yeast culture for yeast and 0.02% of the total soluble protein in transgenic potato plants.