Human peripheral blood cells, especially lymphocytes and thrombocytes, are extensively studied in neuropsychiatric research both as tools for investigating systemic derangements in neuropsychiatric disorders, and as peripheral models for getting information on central nervous system biochemistry. Specific interferon (IFN)-gamma receptors have been found on both human lymphocytes and neural cells. The aim of the present study has been to evaluate IFN-gamma binding on peripheral blood T lymphocytes from parkinsonian patients, as compared with that on blood T cells from healthy subjects. We have found that T lymphocytes from parkinsonian patients bear a significantly smaller amount of IFN-gamma receptors than those from controls. Such IFN-gamma binding sites are of the same type in patients and healthy subjects (Kd (mean +/- SEM): 1.4 +/- 0.07 vs. 1.2 +/- 0.06, respectively). These findings, which are not specific for Parkinson's disease, are discussed in terms of its immunopathogenesis, since it has been reported that activated T lymphocytes have decreased amounts of IFN-gamma receptors.