Abstract: Enzyme activity for a given sample is automatically determined by measuring light-extinction, at each of a succession of "points" in time and involving a plurality of measurements at each such time. At each of these "points" in time, the several individual measurements are made within a period of time which is brief as compared with the period of time between successive measurement points, and mean value and standard deviation are calculated from these individual measurements. A regression curve is drawn through the measurement points thus obtained, the enzyme activity being determined from the slope thereof at a predetermined time. A total measurement error is also calculated at the same time.