Amines form proton-transfer ion pairs of the type BH+ In- with acidic indicator hydrocarbons InH in THF, Relative equilibrium constants measured for a number of amines in THF differ substantially from ionic pK(a) values for BH+ in acetonitrile or DMSO. The results show that ion pair dissociation constants of the protonated amine ion pairs in THF vary by several orders of magnitude and point out that a; the present time amines cannot be placed quantitatively on any of the ion pair acidity scales currently in use for-neutral:acids in THF.