The influence of varying concentrations of Co(dmgh)2, NaOH and axial base on the rate of hydrogenation of fumaric and maleic acids has been studied in detail. Intramolecular hydrogen bonding in the monoanion of maleic acid and the trans orientation of carboxylic acid groups in fumaric acid are important factors which account for the difference in the rate of hydrogenation of these substrates. Mono-, di-and trialkyl amines as axial bases modify the activity of the catalyst, dialkylamines conferring the maximum activity and trialkylamines the least. Back-strain on nitrogen atom and solvation energy of the amines are responsible for their different behaviours. A rate law has been proposed and verified © 1984 Indian Academy of Sciences.