Changes in the physiological index and skill index resulting from long-duration baseball fielding practice were examined to obtain useful suggestions for training. Seven collegiate baseball players participated in fielding practice in the shortstop position. One set fielding practice lasted for 5 minutes at intervals of 17 seconds, and 12 sets were repeated. A rest period of 1 minute was allowed between the sets. As a physiological index, the heart rate (HR) was measured continuously every 5 seconds from 30 seconds prior to the start of the first set to the end of the final 12^th set. The ratings of perceived exertion (RPE) and the blood lactate concentration (La_b) were measured at preinitiation (Pre) of the first set and after the end of each set. As a skill index, the catching score and the throwing score were measured at every trial. The peak HR in each set changed from 173±10 bpm in the third set to 163±10 bpm in the 12^th set. The minimum HR during the rest period fluctuated between 110 and 120 bpm. The mean La_b increased rapidly from Pre until the peak value in the third set (5.7±4.1 mmol/l), and then decreased gradually to the 12^th set (2.2±0.8 mmol/l) ( p <.05). The mean RPE increased rapidly from Pre until the first set (12±2) ( p <.05), and then increased gradually until the peak value in the 8^th set (17±1) ( p <.05), decreasing gradually thereafter until the 12^th set (15±1). In the catching score, the number of attempts at 3 points decreased significantly and the number of attempts at 2 points increased significantly in sets 6-12 in comparison with sets 1-4 ( p <.05, respectively). In the throwing score, the number of attempts at every point did not change significantly. The above results suggest that if fielding practice is continued at the frequency of every 17 seconds for a long duration, high performance can be effectively maintained when 1) fielding practice is divided into sets of several minutes with a short rest period between the sets, 2) a long rest period is interposed between several sets, and 3) carbohydrate is taken between several sets.