The influence of buoyancy on swimming performance was investigated. The center of buoyancy (CB) and center of mass (CM) were statically measured using reaction board techniques. The CB was found to lie cranial to the CM. Males were found to a have a greater distance between their CB and CM (d) than females. This gender difference was significantly related to the amount of adipose tissue in the body. Males swam and kicked faster than females during the middle 13.7 m of a 22.9 m sprint. No relationship was found between performance and d. The size of the gender differences in the static measurements of d was found to depend on the level of submersion, orientation of the body about its long axis (prone and supine), and the level of inhalation. Although the value of d was larger when submerged, the gender difference was smaller. The differences in d for prone and supine postures and different levels of inhalation were also found to be smaller when submerged. The static trials were videotaped using an underwater camera. Joint centers defining 15 segments were digitized to determine the CM. A segmental, volumetric model of the body was applied to these data to determine the CB. The correlations of the indirect and direct measurements of the CB and CM exceeded 0.72 for all trials. The CB and CM were predicted to within 3 cm of their directly measured locations. There was little correlation between the direct and indirect values of d. The indirect measurements of the buoyant force were accurate within 4% and were highly correlated (r = 0.98) for all conditions. The position of the CB fluctuated 20 cm in the cranial-caudal directions during one underwater arm pull such that it moved caudally to the CM location during the stroke. The static measurements of the CB and CM fail to directly support any influence of buoyancy on performance. However, the indirect method has demonstrated previously undocumented dynamic movement of the CB. The amount of movement in the CB suggests that the influence of buoyancy on performance may change substantially during the stroke cycle.