Abstract: We described an improved method for measuring dopamine-β-hydroxylase activity in human plasma.The assay is based on the enzymatic conversion of tyramine to octopamine which is then oxidized to p-hydroxybenzaldehyde.The latter can be determined hv the use of ultraviolet spectrophotometer.Activities are assayed on aliquots of 10～60 μl of human plasma.It is hoped that tee method should prove to be useful in clinical studies and for studies in the field of acupuncture.