Abstract: A procedure for photometric measurement of liquids in a reaction vessel in an automatic analyser, with a radiation flow having its course perpendicular to a row of the reaction vessel, so as to provide a reliable and positively operating measuring method for the photometric measurement of the liquids. The procedure is characterized in that the radiation flow and the reaction vessel are in movement relative to each other during the measurement. The invention affords the advantage of improved accuracy of measurement and improved reliability since it becomes possible, by measuring a moving object and at the same time calculating the mean of the radiant flux over accepted portions of the signal, to eliminate the error of measurement introduced by a dirt particle or by a scratch. The invention also concerns a row of reaction vessels employed in the procedure, wherein each reaction vessel is contiguous to the next and separated by a wall.