The sequestration of [3H]spiperone by lymphocytes was studied in preserved cells obtained from 22 schizophrenic subjects and 40 of their relatives, and the results were compared with those obtained from 25 healthy control subjects. Mean displaceable sequestration values, obtained from measurements made at a single radioligand concentration (1nM) which optimised the relative contribution of "high affinity" sequestration, were found to be similar for all groups of subjects. Furthermore, displaceable spiperone sequestration was abnormally high in only a small proportion of the schizophrenics (13.6%) and their relatives (5%). There was no evidence that either exposure to neuroleptic medication or duration of illness had an effect on sequestration values. The results suggest that, at least until the required experimental conditions are better established, [3H]spiperone sequestration by lymphocytes does not offer a useful vulnerability marker for schizophrenia.