Abstract Five generally applied methods for the estimation of calcium in serum were compared as to their precision, accuracy, speed and productivity. The influence of storage at 4°C and −20°C and of a number of possible interfering factors were also investigated. As a result the continuous flow method with acid dialysis according to H.J. Gitelman (Anal. Biochem., 18 (1967) 521) in the modification of Teehnicon appeared to meet these conditions the most.