In the study aimed at evaluation of the FBS (Frankfurter-Befindlichkeits-Skala) usefulness, participants were 90 schizophrenic patients differing in clinical characteristics. The FBS scale and three other alternative self-rating scales (the P-D scale by von Zerssen, and two simple scales of visual analogies) were administered in this group twice at the interval of about 48 hours. For comparison purposes, three scales of clinical assessment (BPRS, KOSS-C, KOSS-W) were used as well. Obtained results indicate satisfactory reliability, i.e. internal consistency of the FBS (Cronbach alpha = 0.96), and its test-retest stability (tauB = 0.86). Sufficiently high correlations were found between the FBS and each of the alternative self-rating scales used, especially the similar PD-S (tauB = 0.65). Somewhat weaker, but significant correlations with a clinician's assessment (particularly as regards productive symptomatology of the schizophrenic syndrome) and with same clinical variables (meaningful correlations with stage of the illness), as well as an interesting factorial structure of the self-rating scale suggest that the latter may serve as a valid diagnostic tool complementary to clinical evaluation. The scale may be administered to patients sufficiently motivated to fill in the questionnaire, or to those who can be motivated to do so. A shortened version of the scale with good psychometric characteristics may be more convenient. Our findings allow to conclude that the FBS is a useful diagnostic instrument, supplementing clinical assessment of schizophrenic patients' mental status.