Alterations in lymphocyte binding capacity for the dopamine antagonist 3H-spiperone may be of great interest in psychiatric and neurological disorders: an increase in capacity noted in lymphocytes of schizophrenic patients and their families may well turn out to be a phenotypic vulnerability marker. Since the 3H-spiperone binding assay with lymphocytes does not fulfill common receptor-binding assay criteria and depends more on crucial analytical conditions, shortcomings in binding assay might possibly lead to irreproducible results. A detailed methodological description of the binding assay and subsequent calculations has therefore been given in this paper.