The “front‐to‐back discrimination” represents the ability of an underwater hydrophone to favor reception of a desired signal originating in front of the hydrophone by discriminating against a usually undesired signal originating behind the hydrophone. Under normal conditions in a confined measurement area, the value of the front‐to‐back discrimination is influenced to a considerable extent by such measurement factors as conditions of the medium, the directionality characteristics of the projector, and the distance separating the projector and the tested hydrophone. It is reported that reverberation appears to mask the true back‐side response of the hydrophone, and that thermal gradients and possibly unusual natural effects oftentimes limit the validity of some underwater measurements. Data are presented to show that a hydrophone measured with highly directional projectors exhibits a higher front‐to‐back discrimination than if measured with non‐directional projectors. It is also shown that the front‐to‐back discrimination appears to decrease with increasing distance between the projector and the tested hydrophone. These effects are attributed to the absence of a strictly free‐field in a bounded volume of water.