The hydrogenation process of the intermediate valence compounds CeNiAl, CeNiGa, CeNiIn, CeNiSi and CeNiGe and of the Kondo semiconductor stannide CeNiSn has been investigated. Magnetization and electrical resistivity measurements reveal interesting physical transition induced by the insertion of hydrogen: (i) the Kondo temperature decreases from 600(20) to 220(10) K in the sequence CeNiGe --> CeNiGeH1.6(1); (ii) the hydrides CeNiAlH1.93(5) and CeNiGaH1.1(1) contain cerium in trivalent state and the former shows the presence of magnetic correlations around 3.6(2) K; (iii) in contrast, CeNiInH1.8(2) presents a ferromagnetic transition at T-C = 6.8(2) K and a magnetic transition Kondo semiconductor --> antiferromagnet (T-N = 4.5(2) K) --> ferromagnet (T-C = 7.0(2) K) is evidenced in the CeNiSnHY system. These results are explained by a modification of the competition between RKKY magnetic interaction and Kondo interaction induced by the hydrogenation of these intermetallics. (C) 2004 Elsevier B.V. All rights reserved.