The validity of probe-tube microphone measurements in providing data indicative of the magnitude of the change in the psychoacoustic experiences of subjects resulting from changes in earmold configuration was investigated. The relationship between these measures in the real ear canal and those changes observed in 2-cc and Zwislocki couplers under similar circumstances of earmold modification was also measured. Standard, vented and “open” earmold conditions were utilized. Threshold and probe-tube measurements were made sequentially without moving the earmold at 21–29 discrete frequencies. Statistical evaluation revealed that these two techniques did not produce significantly different results except at 125–165 Hz where noise masking may have been a factor influencing the threshold data. Neither coupler as used gave an accurate quantitative estimate of the effects of vented earmolds or the open earmold configuration but the Zwislocki coupler gave a somewhat better approximation than the 2-cc coupler. [Work supported by NIH.]