Sensitivity to interaural timing differences (ITDs) at high frequencies has largely been attributed to slow amplitude modulations (AM) in the envelope. However, in noisy situations, high-frequency signal envelopes can easily be corrupted making AM less useful for sound localization. Previous work has shown that frequency modulation (FM) introduced into a high frequency pure tone can also yield sensitivity to ITDs. This suggests that FM may be an additional cue used by the auditory system to resolve high-frequency ITDs, which may be useful in noisy situations. This experiment tests the hypothesis that in-phase AM and FM are complementary cues that improve ITD sensitivity at high frequencies in the presence of noise. A 4-kHz tone stimulus with a fixed ITD of 500 μs was used, and had either 200 Hz AM, FM or in-phase AM + FM imposed. The signal-to-noise ratio (SNR) needed to achieve 70.7% correct in a left-right discrimination task was measured. Results showed that the SNR needed for FM was typically lower than AM, and AM + FM was significantly lower than either AM or FM alone. The results suggest that in-phase AM and FM may provide complementary cues that aid in discriminating ITDs at high frequencies in the presence of noise.