Psychophysical tuning curves were obtained from Old World monkeys via a positive reinforcement operant procedure. These tuning curves were found in two different manners. In the first, simultaneous tone‐on‐tone masking was utilized, while the second procedure involved a forward masking paradigm. In this condition, the subjects' task was to detect brief (30 ms) tone pulses which followed each of a train of masking pulses. With both paradigms, threshold masker levels were determined by a tracking procedure. In comparing the two types of curves, it was found that the forward masking tuning curves were generally more sharply tuned than were the simultaneous masking tuning curves at a given frequency. This fact was verified by computingQ10values for the individual curves, as well as by a comparison of the slopes of the tuning curves under the two masking conditions.