Elements can exist in both stable and unstable (radioactive) forms. Most elements of biological interest (including C, H, O, N, and S) have two or more stable isotopes, with the lightest of these present in much greater abundance than the others. Among stable isotopes the most useful as biological tracers are the heavy isotopes of carbon and nitrogen. For more than 20 years, OlChemIm has specialized in the development, production, and marketing of stable (non-radioactive) isotopes and phytohormones labelled with stable isotopes.