The purpose of the present study is to observe the effects of body tilting on circulatory responses and forearm muscular endurance. Thirty-four subjects participated in the study. Body positions used in this study were three kinds : horizontal-supine, head-down and head-up positions. Each subject performed hand grip exercise in three different body positions. Forearm and lower leg blood flow was measured by using mercury-in-rubber strain-gauge method. Blood samples were obtained from cubital vein and brachial artery in selected ten subjects. The results were summarized as follows: 1. The significant difference in forearm resting blood flow was observed among three body positions (p < 0. 05). 2. In the case of work load of 1/3 of maximal grip strength, significant difference in performance was not observed among three body positions, but in 1/6 of max. strength, significant difference was observed between head-up and other two body positions. 3. As to the forearm peak blood flow, difference between head-up and other two body positions was statistically significant (p<0.05). 4. Blood lactate and arterial-venous oxygen difference immediately after exercise (work load of 1/3 max. strength) showed the highest value in head-up position compared with other body positions. 5. Circulatory responses accompanying body tilting seem to have influence on muscular work capacity. The longer the work time is, the more remarkable the influence seems to be.