This study evaluated frequency discrimination ability in 11 monkeys over an extended period of time using a repeating‐standard procedure and the method of constant stimuli. The intersubject variability of the difference limens for frequency (ΔF) was large, as reported by other investigators, but similar in magnitude to the variability of the difference limens for intensity (ΔI) from three of the same subjects in an intensity discrimination experiment. Continued training generally resulted in a rapid decrease in ΔF’s, followed by a longer‐term, slower decrease. For one subject ΔF’s slowly decreased throughout a 190‐week time period. This long‐term training effect was specific to frequency discrimination; a similar effect was not observed for the same subject tested in an intensity discrimination experiment. Finally, ΔF’s from the well‐trained monkeys of this study were larger than monkey ΔF’s from this laboratory reported in an earlier study, and than human ΔF’s. An anatomical explanation for the human/monkey ΔFmagnitude difference is explored.