Recently we developed a useful 12-min submaximal run test at an intensity regulated by ratings of perceived exertion in order to indireclty assess an individual's cardiorespiratory fitness. The purpose of the present study was to evaluate the validity and reliability of the 12-min submaximal run test as a convenient measure of maximal oxygen uptake (VO_2max) and anaerobic threshold (VO_2AT). The subjects were 103 men aged 22.0±2.6 years. All were asked to run for 12 min at an intensity corresponding to 13 on the Borg scale of perceived exertion, and their VO_2max and VO_2AT were measured on the treadmill by means of a graded exercise test (GXT). Pearson's product-moment correlations of 12-min submaximal run distance (2658±321m) with VO_2max (55.8±6.3ml / kg / min) or VO_2AT (40.4±7.0ml / kg / min) were found to be statistically significant (r=0.78 and r=0.76, respectively). The test-retest reliability coeffient of the 12-min submaximal run test on the 18 subjects selected voluntarity was 0.90. VO_2max and VO_2AT values were predicted from the results of the submaximal 12-min run using the prediction equation described by Nakagaichi et al. (1996) (Predicted VO_2max=56.1±6.3ml / kg / min, Predicted VO_2AT=43.7±6.9ml / kg / min). On VO_2max, the validity coefficient was r=0.80, standard errors of the estimate (SEE)=3.75ml / kg / min (SEE%=6.7%), and Error=3.93ml / kg / min. Similar results were obtained on VO_2AT ; r=0.78, SEE=4.37ml / kg / min (SEE%=10.8%), and Error=5.57ml / kg / min. There were no significant differences between measured VO_2max and VO_2AT and their predicted values. From heart rate (HR) data measured during the 12-min submaximal run test on 39 subjects selected randomly, the intensity of the run test was found to range from 85%HRmax to 90%HRmax, although the intensity was significantly higher than the AT. Furthermore, there was no significant difference between %HRmax in the latter half of the 12 minutes of the run test and %HRmax corresponding to RPE13 during GXT. These results suggest that the 12-min submaximal run test is a valid and reliable field test for young adult men. Finally, we attempted to redevelop equations for predicting VO_2max and VO_2AT from the distance covered in the 12-min submaximal run and age using the data from thase subjects : VO_2max=0.015X_1 (m)-0.46X_2 (yr) + 25.14 (R=0.80, SEE=3.77ml / kg / min)VO_2AT=0.017X_1 (m) -0.51X_2 (yr) + 7.53 (R=0.78, SEE=4.39ml / kg / min)X_1=Distance (m), X_2=Age (yr).