The hydrolysis of nicotinamide in alkaline solutions was studied. An ammonia gas-sensing electrode was used to follow the formation of ammonia. A technique making use of simulated reactions has been developed to calibrate the electrode under dynamic conditions overcoming problems arising because of the relatively slow response of the sensor. A general expression has been derived for the pseudo first-order rate constant valid over the concentration range 0.005 to 0.10 M nicotinamide, 0.1 to 0.5 M hydroxide and the temperature range 22° to 31° C, under constant ionic strength (0.5 M NaOH + NaC1O4).