The loudness for pure tones was measured by loudness matching for 1-s pure tones from 100 to 50<th>000 Hz. The standard tone was 1000 Hz. Subjects were instructed to match the loudness of the comparison tone at one of the test frequencies to the loudness of the standard tone. The standard was presented at one of five sound pressure levels (SPL) for each set of frequencies. The standard SPL was varied randomly across test series. The subjects were bareheaded US Navy divers tested at a depth of 3 m. All subjects had normal hearing. The tones were presented to the right side of the subject from an array of underwater sound projectors. The SPL was calibrated at the location of the subject’s head with the subject absent. The loudness increased more rapidly as a function of standard SPL at mid-frequencies than at either high or low frequencies. The most compact loudness contours (least SPL change across range of standard SPL) were at 50<th>000 Hz. The underwater loudness contours across frequency are significantly different from in-air measurements and have a minimum in the 1000 Hz region rather than the 2–4 kHz region observed for in-air measurements. [Work supported by ONR.]