The purpose of this study was to investigate the effects of low-intensity endurance training on the lactate threshold (LT) and the onset of blood lactate accumulation (OBLA), as well as the relationship among blood lactate, heart rate, systolic blood pressure and the plasma noradrenaline (NA) concentration during submaximal exercise before and after training. Seven middle-aged women aged 33-57 years performed endurance training on a bicycle ergometer for 60 min 3 days a week for 6 weeks at an intensity corresponding to 50% of their maximum oxygen uptake. The results were summarized as follows: 1) LT and OBLA increased significantly by 32% (p less than 0.05) and 16% (p less than 0.05), respectively, after the training. 2) The increase rate of OBLA correlated negatively to its initial level (p less than 0.05) but the increase rate of LT did not. 3) Heart rate, systolic blood pressure and the pressure rate product (systolic blood pressure x heart rate x 10(-2] at LT and OBLA did not change significantly after the training. 4) A significant linear correlation between blood lactate and NA was observed during the submaximal exercise before (p less than 0.05) and after (p less than 0.05) the training, but the slopes of the two regression lines did not differ significantly. It was concluded that low-intensity training results in a significant improvement in LT and OBLA for middle-aged women. It was further suggested that, after the training, diminished responses of the cardiovascular and sympathetic nervous system are in parallel with the decrease in the blood lactate concentration during submaximal exercise.