The complexes trans-PtHL(PEt3)2, where L is an o-, m-, or p- substituted benzoato-ligand or a substituted acetato-ligand, have been prepared and their 1H n.m.r. spectra have been determined. Linear correlations are found between the chemical shift of the hydrido-ligand, the platinum–hydrogen coupling constant, the platinum–hydrogen stretching frequency, and the pKa of the parent carboxylic acid. These are discussed.