Plasma neuroleptic levels of 31 elderly psychiatric patients (8 males and 23 females, age 80.1 +/- 8.95 years) on chronic propericiazine therapy and with multimorbidity were measured by means of radioreceptor assay. There was no significant correlation between the daily dose and the plasma neuroleptic level. Nor was there any significant correlation between the patients' age and the ratio of plasma neuroleptic level to the daily dose. On the other hand, the immobility score of patients (GBS scale) had a high correlation with the ratio of the plasma neuroleptic level to the daily dose. Furthermore, patients with positive C-reactive protein (CRP) had an average ratio value 3-fold higher than the CRP negative group. The results suggest that the plasma neuroleptic level of propericiazine in elderly patients is raised by morbidity and immobility rather than chronological age per se.