Monaural and binaural thresholds of 10 listeners were detd. for a 1000-cycle tone and for a "white" noise. For each of the observers, the binaural threshold was found to be significantly lower than the monaural threshold when the 2 ears were "equated" in sensitivity. The difference between the monaural and binaural thresholds was found to be significantly greater for the pure tone than for the noise. Monaural and binaural thresholds were detd. with the 2 ears "equated" in sensitivity and with the 2 ears "mismatched" in sensitivity by fixed ratios. It was found that the difference between the binaural threshold and the threshold of the better ear decreased as the difference in the effective stimulation at the 2 ears was increased. The difference between the binaural threshold and the threshold of the better ear was found to be not statistically significant when the 2 ears were stimulated at sensation levels more than 6 db apart. The results of the present study fail to confirm the hypothesis that the auditory threshold is constant and equal to the sum of the effective acoustic powers at the 2 ears. For most of the observers, the difference between the monaural and binaural thresholds was found to be significantly less than would be predicted by this hypothesis.