The aim of this study was to compare the effects of two high-intensity, treadmill interval-training programs on 3000-m and 5000-m running performance. Maximal oxygen uptake (V̇O2max), the running speed associated with V̇O2max (vV̇O2max), the time for which vV̇O2max can be maintained (Tmax), running economy (RE), ventilatory threshold (VT) and 3000-m and 5000-m running times were determined in 27 well-trained runners. Subjects were then randomly assigned to three groups; (1) 60% Tmax, (2) 70% Tmax and (3) control. Subjects in the control group continued their normal training and subjects in the two Tmax groups undertook a 4-week treadmill interval-training program with the intensity set at vV̇O2max and the interval duration at the assigned Tmax. These subjects completed two interval-training sessions per week (60% Tmax=six intervals/session, 70% Tmax group=five intervals/session). Subjects were re-tested on all parameters at the completion of the training program. There was a significant improvement between pre- and post-training values in 3000-m time trial (TT) performance in the 60% Tmax group compared to the 70% Tmax and control groups [mean (SE); 60% Tmax=17.6 (3.5) s, 70% Tmax =6.3 (4.2) s, control=0.5 (7.7) s]. There was no significant effect of the training program on 5000-m TT performance [60% Tmax=25.8 (13.8) s, 70% Tmax=3.7 (11.6) s, control=9.9 (13.1) s]. Although there were no significant improvements in V̇O2max, vV̇O2max and RE between groups, changes in V̇O2max and RE were significantly correlated with the improvement in the 3000-m TT. Furthermore, VT and Tmax were significantly higher in the 60% Tmax group post- compared to pre-training. In conclusion, 3000-m running performance can be significantly improved in a group of well-trained runners, using a 4-week treadmill interval training program at vV̇O2max with interval durations of 60% Tmax.