Seven N-alkylmaleamic acids were synthesized and converted through heating to the corresponding N-alkylmaleimides. Alkylmaleimides of varying chainlength were shown to effectively inactivate yeast alcohol dehydrogenase at pH 7.0. The effect of pH on the rate of hydrolysis of N-ethylmaleimide was studied in the pH range from 8.6 to 9.4 where specific base catalysis of the reaction was observed. Second-order rate constants for maleimide inactivation of yeast alcohol dehydrogenase were shown to increase with increasing chainlength of the alkyl substituents of the maleimide derivatives. A chainlength effect was not observed in the reaction of N-ethylmaleimide and N-heptylmaleimide with cysteine and glutathione. Yeast glucose 6-phosphate dehydrogenase, which is less sensitive to maleimide inactivation than is yeast alcohol dehydrogenase, was inactivated by both N-ethyl and N-heptylmaleimide at rates indicating no appreciable chainlength effect.