We adapted a previously described method for the measurement of transthoracic tissue thickness and volumes of blood and interstitial tissue. This non-invasive procedure can be performed safely and by relatively simple means. We used a gamma camera and 99mTc to obtain transmission and emission scintigrams. A computer program written for a personal computer, can recognize the borders of the lung in a fully automatic manner and do the necessary calculations. Clinical studies show significantly higher interstitial volumes of the lung in patients with chronic pulmonary sarcoidosis.