A series of experiments was undertaken to systematically study one aspect of binaural interaction for dichotic-ally presented clicks the end point of lateralization, which is referred to in this paper as the lag-click threshold (Δt2). The results of experiments in which click parameters were manipulated are presented in Sec. III. These results indicate that the lag-click threshold is decreased by an increase in the sensation level (SL) of both clicks, by an interaural intensity asymmetry favoring the lag click, or by a decrease in the low-frequency components of both clicks. The results of experiments in which the background-noise parameters were manipulated appear in Sec. IV. As the SL of binaural broad-band noise (125-8000 cps) is increased to 30 dB, the lag-click threshold decreases; but as the noise level is increased further, the lag-click threshold increases. The finding of a minimum point at 30 dB is related to the broad spectrum of the noise. One-octave bandwidths of noise produce monotonic functions. A 1-oct low-frequency band of noise presented either to both ears or to the ear receiving the lead click, decreases the lag-click threshold, while a 1-oct high-frequency band of noise presented either to both ears or to the ear receiving the lead click increases the lag-click threshold. Finally, a 1-oct low-frequency or high-frequency band of noise presented to the ear receiving the lag click produces a substantial increase in the lag-click threshold. The results are discussed briefly in terms of the available physiological literature and a model is proposed.