Several C2H3O- species resulting from the interaction of acetylene and hydroxide have been characterized with nb initio calculations. MP2 geometry optimizations were performed with augmented, correlation-consistent, polarized-valence, double-zeta basis sets. The total energies of the most crucial structures were also recalculated at the QCISD(T) level with MP2-optimized geometries. Nine structures corresponding to local minima have been found at the MP2 level, their stability decreasing in the following order : acetaldehyde enolate anion > acetyl anion approximate to ethynide-water complex > ethenyloxy anion approximate to vinyloxy anion. ethynide-water complex is either the most stable product of the reaction of hydroxide with acetylene or at least an initial stable intermediate.