Dedicated to Prof. Tino Giiumann on the occasion of his 6OCh birthday (25.V11.85) ~~ 4-Aryl-2,3-dioxobutyrdmide hydrates 1 undergo the benzil-benzilic acid rearrangement to form (substituted) benzyltartronate monoamides 2. For compound l a (Ar = Ph), it is demonstrated by isotopic labelling that the reaction occurs exclusively by migration of the CONH, group. Kinetic measurements with la-c and with the cyclic amide quinisatine 6 show that the rearrangement of the carboxamide group, proceeding via an alkali-catalysed step, can reach a plateau in the kOb,./[OH-] diagram (cf: the Fig.), due to complete formation of a mono-anion, and a further increase of rate attributable to the rearrangement of a bis-anion. Comparisons suggest that rearrangements involving an amide group are slower than those involving an ester group, and that, for this effect (as for others), the pre-equilibrium deprotonation of the hydrate is more important than a specific migration tendency.