The authors studied in 50 healthy subjects the cilindroid and the planimetric method for the radiological measurement of TLC. Both methods proved to be accurate, but the first showed a better relation with the pletismographic measurements; in both methods the individual variability was very limited (5 divided by 6%). In a screening protocol comprising double-projection chest X-ray, the radiological measurement of TLC seems to be very useful to evaluate with simplicity and realiability its values and its variations in time.