Abstract: This paper describes the principle of a method through which the NAD/NADH-dependent reactions can be visualised with Meldola blue, so that measurements can be made more sensitive. It describes the applications of the method to the determination of LDH and αHBDH activities in serum with a continuous flow analyzer.. It shows the correlation with the results obtained on a centrifugal analyzer., and discusses the increase in sensitivity, the reduction in cost and the ease of application of the method.