The mean velocity of 9 out of 10 women's events during the U.S. Olympic Swimming Trials was greater in 1984 as compared to 1976. Three of the 10 men's events showed improvement. In 9 out of these 12 events, the increased velocity was accounted for by increased distance per stroke (range, -3 to -13%). In the women's 100-m butterfly and 100-m backstroke, increased velocity was due solely to faster stroke rates. The finalists in each event were compared to those whose velocities were 3-7% slower. In almost all events and stroke styles, the finalists achieved greater distances per stroke than did the slower group. In the men's events increased distance per stroke was associated with decreased stroke rate, except in the backstroke, in which both were increased for the finalists. Although the faster women swimmers generally had greater distances per stroke, they were more dependent than men on faster stroke rates to achieve superiority. The profile of velocity for races of 200 m and longer indicated that as fatigue developed the distance per stroke decreased. The faster swimmers compensated for this change by maintaining or increasing stroke rate more than did their slower competitors. This study indicates that improvements and superiority in stroke mechanics are reflected in the stroke rate and distance per stroke used to swim a race.