Among different types of labeling, C-13-labeled compounds are the most demanding in organic chemistry, life sciences and materials design. However, C-13-labeled organic molecules are very difficult to employ in practice due to extreme cost. The rather narrow range of labeled organic starting materials and the absence of universal synthetic building units further complicate the problem and make utilization of C-13-labeled molecules hardly possible in many cases. Here we report a versatile approach for C-13(2)-labeling of organic molecules starting with C-13 elemental carbon: C-13 carbon is applied for the synthesis of calcium carbide ((CaC2)-C-13), which is subsequently used to generate acetylene - a universal C-13(2) unit for atom-economic organic transformations. Syntheses of labeled alkynes, O,S,N-functionalized vinyl derivatives, polymers and pharmaceutical substances were demonstrated. Elemental C-13 carbon, as the chemically most simple source for C-13(2)-labeling, here was successfully combined with universal synthetic applicability of alkynes.