The catalytic nature of the process of cathodic hydrogenation of the unsaturated bond has been determined by evaluating radiometrically the influence of addition of different quantities of Ni-63 to the supporting solution free from nickel ions on the unsaturated bond hydrogenation rate. The catalytic activity of a nickel cathode used to hydrogenate 2-butynediol-1,4 labelled by a C-14 isotope is approximately four times higher in a nickel-plating electrolyte than that in an electrolyte free from nickel ions. Electrolysis conditions determine the extent of triple bond reduction, the quantity of unsaturated glycols in the coating and its physical and mechanical properties. When using the mixture of acetylenic and ethylenic glycols, a bright, highly plastic (to 6%) coating is deposited from the nickel-plating electrolyte. The intermediate ethylene may be quantitatively synthesised in the nickel-plating bath.