1. The influence of amines and heterocyclic compounds containing nitrogen on the rate and selectivity of the hydrogenation of cyclopentadiene, tolane, and dimethylvinylethynylcarbinol was studied in the presence of a skeletal nickel catalyst. 2. In the presence of methylamine, butylamine, ethylenediamine, hexamethylenediamine, piperidine, 4-ethylpyridine, benzotriazole, and quinoline methiodide, cyclopentadiene, tolane, and dimethylvinylethynylcarbinol are selectively hydrogenated on a skeletal nickel catalyst to the corresponding monoolefinic compounds. Such selectivity may be explained by the reversible adsorption poisoning of the catalyst. 3. In the presence of α-naphthylamine, diethylamine, diphenylamine, and 2-ethylpyridine, the hydrogenation of cyclopentadiene, tolane, and dimethylvinylethynylcarbinol is nonselective; the monoolefinic compounds formed are hydrogenated further, forming the fully hydrogenated compounds.