The influence of tributylphosphine, diethyl ether, carbon monoxide, n-butanethiol, dimethyl sulphate and tert.-butyl chloride in the hydrogenation of 1-butene and 1,3-butadiene on platinum catalysts was studied. The effect of carbon monoxide and tert.-butyl chloride on the hydrogenation rates of 1,3-butadiene and 1-butene was measured. In contrast to piperidine, which decreases much more the 1-butene hydrogenation rate, carbon monoxide and tert.-butyl chloride decrease this rate equally or even increase it compared with that found for 1,3-butadiene. The influence of the above compounds on the mechanistic selectivities, i.e. direct formation of butane ( S p BA) and 1,2-addition ( S p 1.2), and on the thermodynamic selectivity, i.e. the ratio of the consecutive transformation rate of 1-butene to its formation rate ( S c), was studied for 1,3-butadiene hydrogenation. The effect of tributylphosphine on S p BA and S p 1.2 is similar, although attenuated, to that of piperidine,i.e. S p BA dimethyl sulphate and tert.-butyl chloride on S p BA and S p 1.2 are negligible or opposite to that of piperidine and tributylphosphine, i.e. S p BA increases and S p 1.2 decreases. The same trend is observed with the trans/cis ratio and S c, which decrease, contrary to the effect of piperidine. All these effects are rationalized by considering two classes of compounds, one including the donor ligands (containing N and P) and the other including the acceptor ligands (containing O, S and Cl). In general, the results are consistent with an electronic origin of all the effects observed. A survey of the results and of the mechanisms published in the literature allowed a coherent interpretation of the experimental results to be proposed. Such an interpretation could give new ideas for experimental mechanistic studies.