Perceptual learning was used to examine mechanisms of pitch perception. Thresholds (F0DLs) were measured for discrimination of the fundamental frequency (F0) of complex tones with a nominal F0 of 100 Hz and cosine-phase or random-phase harmonics. Tones were bandpass filtered and presented in threshold equalizing noise. A group trained using stimuli with the filter centered on LOW harmonics (1–5) showed a large training effect, with transfer to stimuli with MID harmonics (11–15) or MID-HIGH harmonics (14–18), but no transfer to stimuli with HIGH harmonics (28–32). A group trained with MID or MID-HIGH stimuli showed a large training effect, with transfer to the LOW stimuli and no transfer to the HIGH stimuli. A group trained with HIGH stimuli showed no training effect for any stimuli. The results suggest that similar mechanisms were used for F0 discrimination of the LOW, MID, and MID-HIGH stimuli, and that a different mechanism was used for the HIGH stimuli. It is proposed that the LOW, MID and MID-HIGH stimuli were discriminated using temporal fine structure (TFS) information, in the former case TFS information about individual resolved harmonics, and in the latter two cases TFS information about the periodicity of the waveform evoked by interfering harmonics.