1. The most important properties of a rating instrument aimed at detecting possible changes in psychopathology are as follows: a) communicability to not yet experienced raters; b) satisfactory levels of reliability and validity; and c) sensitivity to changes. Since its construction some years ago these properties of the Comprehensive Psychopathological Rating Scale (CPRS) have been investigated in several sessions, both experimental, and in the course of clinical drug trials. 2. Raters with a different training background (physicians, psychologists, social workers, nurses), and a different level of experience in ratings have participated in the sessions. 3. In all instances the CPRS has proved to be highly reliable and highly sensitive. It appeared to be easily communicable, also in its international versions, and its content seems to fit very well with different cultural contexts. Information about its validity has been inferred from the studies mentioned above, and, also from correlations with other well known rating instruments.