Just-noticeable differences (jnd's) for frequency of complex waves with stable F0 are 0.3--0.5 Hz [Flanagan and Salow (1958)]. However, there are both articulatory and acoustic reasons to believe that jnd's are greater during breathy phonation than during modal phonation. This study investigated pitch discrimination during breathy phonation by manipulating acoustic parameters. Both breathy vowels and modal vowels from Mazatec were digitized. Intensity was equalized, and F0 was manipulated by 0.2-Hz increments employing the OCEAN Speech Processing Program, while all other acoustic parameters were held constant. Subjects listened to pairs of these stimuli and judged whether they were the same or different. It is predicted that jnd's would be greater during breathy phonation than during modal phonation. Results will be discussed with reference to laryngeal timing patterns in vowels in Mazatec and elsewhere. In Mazatec, tone and breathy phonation are sequenced with respect to each other on a single vowel. In languages that possess phonation contrasts without tonal contrasts [e.g., Gujarati: Fischer-Jorgensen (1971)], no sequencing is observed: breathiness pervades the vowel. It is likely that pitch discrimination plays a contributing role in such timing distinctions between Mazatec-type languages and Gujarati-type languages: Pitch is likely to be less discriminable during breathy phonation.