The effects of hydrogenation on the structural transitions in C-60 and its isomers are investigated from first principles. C60H2 and C60H60 are used as paradigmatic examples. We find that hydrogenation enhances the stability of the isomers and it reduces the barriers for structural transitions through Stone-Wales bond rotations. The reduction is due to sp(2) bonding of the rotating pair of carbon atoms at the transition state. The calculated barriers for the in-plane Stone-Wales process are 6.03 and 5.30 eV for C60H2 and C60H60, respectively. Published by Elsevier B.V.