The dissociation constants of the cyanohydrins of a series of methylcyclohexanones have been measured. The polymethylcyclohexanone cyanohydrins show increasing instability on substitution owing to the effects of "axial crowding". The cyanohydrins of 3- and 4-methylcyclohexanone were found to be more stable than that of cyclohexanone and to explain this a new concept of "equatorial interference" is introduced.