The purpose of this study was to determine if finger tip capillary blood hematocrit is a valid estimate of anticubital venous blood hematocrit at rest and after submaximal exercise. Simultaneous samples of finger tip cpaillary and venous blood were drawn from thirty-one subjects (15 males, 16 females) before and after a 15 min submaximal exercise on a bicycle ergometer. Venous and capillary blood hcts. were 42.0% +/- 3.9 and 42.0% +/- 3.5 respectively before exercise and 43.3% +/- 3.5 and 42% +/- 3.8 after exercise (X +/- s). The regression equation for predicting venous hct. from finger tip capillary blood after exercise was: Hctv = 0.87 Hctc + 6.44 with r = 0.95 (P less than 0.05). The results indicate that the finger tip capillary microhematocrit method is a valid indicator of venous blood hct. following exercise.