The purpose of this study was to compare the differences of cardiorespiratory functions and blood constituents in high school middle distance runners. Thirty nine high school male students composed with 13 excellent-runners, 13 good-runners and 13 non-runners were recruited for this study, The measurements were conducted on some factors of cardiorespiratory functions and blood constituents. The results of this study are as follows; 1. In the cardiorespiratory functions, excellent-runners group and the good-runners group were significantly lower than the non-runners group in HRrest and HRmax, but higher in VO₂max and exercise duration, and the excellent group was higher than the other two groups in AT and ％VO₂max. 2. In the blood constituents, the excellent-runners group was significantly higher than the non-runners group in TC, TG and HDL-C and the excellent-runners group and non-runners group were higher than the good-runners group in Hct only among blood constituents. Therefore these results suggest that middle distance running performance is based on many factors and especially it is required to improve VO₂max AT and ％VO₂max in cardiorespiratory functions, and HDL-C and Hct in blood constituents.