To determine the effects of 12 wk of strength training on lactate threshold (LT) and endurance performance, 18 healthy untrained males between 25 and 34 yr of age were randomly assigned to either strength training (N = 10) or control (N = 8) groups. Despite no changes in treadmill VO2max or cycle peak VO2, a 33 +/- 5% increase (P less than 0.001) in cycling time to exhaustion at 75% of peak VO2 was observed following training. No significant changes in cycling time were observed in the control group. There were significant reductions in plasma lactate concentration at all relative exercise intensities ranging between 55 and 75% of peak VO2 training. The improved endurance performance was associated with a 12% increase in LT (r = 0.78, P less than 0.001). The strength training program resulted in significant improvements (P less than 0.001) of 31 +/- 5% and 35 +/- 7% in isokinetic peak torque values for leg extension and flexion, respectively, at a velocity of 30 degrees.s-1. There were also significant increases in 1-RM values of 30 +/- 4% (P less than 0.001) for leg extension, 52 +/- 6% (P less than 0.001) for leg flexion, and 20 +/- 4% (P less than 0.001) for the bench press. These findings indicate that strength training improves cycle endurance performance independently of changes in VO2max. This improved performance appears to be related to increases in LT and leg strength.