A method for calibrating machines suitable to effect an analysis of a blood sample by measuring the erythrocyte sedimentation rate (ESR) and/or aggregation of the red corpuscles, wherein the measurement is effected by exploiting the optical density kinetics obtained from the measurement of the variation in the optical density of the blood sample in an interval of time, to include measuring in which, by the same machine with which the measurement of the optical density is effected on the blood sample, a measurement is effected of the optical density of two latexes, or turbidimetric samples. Each of the two latexes has a known optical density that is reproducible, measurable and different from each other. The method also calibrates in which the difference is calculated between the values of optical density of the latexes as obtained from the measurement performed by the machine and the known values of optical density, to determine at least one correction factor usable to calibrate machine.