This study has focussed on a 10-item Brief Psychiatric Rating Scale (BPRS) subscale for the quantification of schizophrenic states. Seven psychiatrists interviewed jointly patients who all fulfilled the DSM-III criteria of schizophrenia, and in a subsequent pencil-and-paper procedure a judgment analysis was performed. The reliability analysis showed that less experienced BPRS raters made less consistent judgments implying the cautionary statement that the proper use of a scale for schizophrenia requires specialized training with the scale. The validity analysis showed that the BPRS items had an additive relationship implying that the sum of these items is a sufficient statistic for the measurement of severity of schizophrenic states. Finally, the results seem to indicate, that the underlying dimension defined by the 10-items BPRS subscale includes hierarchically the negative and positive symptoms of schizophrenia.