The electroreduction of acetophenone on mercury in acetate buffer (ph 4·8) yields two main products: the racemic mixture of the alcohol (II) and the pinacol (III). Addition of quinidine or some other related alkaloids to the reaction mixture has two effects: the two enantiomers of the alcohol are formed in unequal amounts and the relative yield of alcohol to pinacol is increased. The optical yield reaches a maximum at a potential of −1·8 V ( mse) and increases with decreasing temperature. The ratio of alcohol to pinacol increases with increasing negative potential and with decreasing temperature. The optical yield depends also on the structure of the alkaloid; different diastereoisomers induce optical rotation of the product in opposite directions. There is no correlation between the ability of the alkaloid to induce optical activity and its ability to cause catalytic hydrogen evolution. Induction of optical activity was associated with adsorption of a species which exists only when both acetophenone and the alkaloid are present. The effect of quinidine on the ratio of alcohol to pinacol formed is probably due to the reduction of the surface concentration of the radical intermediate (Ia) and to the reduction of the surface mobility of this species.