The effect of masking noise on binaural interaction of disparate stimuli was studied. Stimuli were trains of pulses and trains of clicks. With continuous noise added monaurally to noise bursts, more noise was required to prevent fusion when the stimulus in the opposite ear was a noise burst than when it was a pulse. In neither case did the level of noise necessary to prevent fusion make the noise burst inaudible. In fusion of noise bursts and pulses, the level of noise added to pulses necessary to prevent fusion equalled the level which made the pulses indetectible. In another experiment, subjects were presented with trains of single pulses at one ear and closely-spaced pairs of pulses at the other. They were required to fuse the single pulse with the second of the pair of pulses. It was found that the addition of noise to the pair of pulses reduced the minimum interpulse interval at which this was possible. These results are interpreted in terms of a mechanism of binaural fusion which compares the strength of the short-term integrated neural response from the two sides. This model receives support from previous electrophysiological observations. [Work at MIT supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research), and the U. S. Navy (Office of Naval Research).]