When rabbit aortic strips were incubated under anaerobic conditions (at 37℃ for 3 hours), the lactate level increased remarkably to about 10 times the level observed under aerobic conditions. In the process of lactate accumulation, the activity of phosphofructokinase increased by 5-30% of the enzymatic level observed under aerobic conditions. When adrenaline was added to the bath medium, the aortic muscle contraction was somewhat weak and the activation of phosphofructokinase was less remarkable in comparison with observations under aerobic conditions. This finding suggests that lactate accumulation in rabbit aorta suppresses the activation of phosphofructokinase in the contracting materials.