The aim of the present work is to determine the conditions of high resolution and precise application of the classical microdensitometers to the evaluation of autoradiographic images. The conclusions have been materialized in the improvement of the mechanical microdensitometer developed in our laboratory some years ago. The original model of this instrument was introduced at the VII. International Symposium on Autoradiography in Zakopane 1974. Since then some modifications have been made on the instrument in order to reach optimum performance.