In order to establish reference equations for prediction of the total distance walked during six minutes (6MWD) for healthy adults, we administered the standardized 6-min walk test to 117 healthy men and 173 healthy women, aged 40 to 80 yr. Oxygen saturation (SaO2), pulse rate, and the degree of dyspnea (Borg scale) were determined before and at the end of the walk. The median distance walked was 576 m for men and 494 m for women. The 6MWD was significantly less for men and women who were older and heavier, and for shorter men. The resulting gender-specific regression equations explained about 40% of the variance in the distance walked for healthy adults: for men, 6MWD = (7.57 x heightcm) - (5.02 x age) - (1.76 x weightkg) - 309 m, and for women, 6MWD = (2.11 x heightcm) - (2.29 x weightkg) - (5.78 x age) + 667 m. These reference equations may be used to compute the percent predicted 6MWD for individual adult patients performing the test for the first time, when using the standardized protocol.