Rate data for reactions of XC6H4CSNMeC6H4Y in methanol at 373 K are presented. The thioamides are less reactive than their oxygen analogues. Linear Hammett plots were obtained for both series (series A: X = variable, Y = 4?-NO2; series B: X = 4-NO2, Y = variable), with p values similar to those obtained for related oxyamides. There is a general trend to higher activation energies but more favourable entropies in the thioamides. The results are interpreted in terms of rate-determining breakdown of a tetrahedral intermediate, irrespective of the nature of X and Y.