Physical acoustics reveals a number of stimulus correlates of sound source distance. Quantitative estimates of these stimulus correlates are compared with appropriate psychophysical thesholds. Such comparisons show that most of these stimulus correlates can, with various restrictions, provide distance information detectable by the ear(s). The stimulus correlates dealt with at greatest length are: intensity, frequency spectrum at near and far distances, binaural intensity ratio, and interaural phase (or time) differences. Problems relating to the use of some of these stimulus correlates as cues are discussed. Other possible distance cues are briefly mentioned. The possible use of much of the available physical information in making distance judgments has not yet been adequately evaluated in psychophysical studies. (48 ref.)