CSF from Parkinson's disease (PD) patients undergoing autologous transplantation of adrenal medulla tissue into their lateral ventricle was examined for the presence of IgG. CSF from 6 of 7 patients incubated with rat brain tissue reacted immunocytochemically to neuronal cell bodies in the substantia nigra and ventral tegmental region. This reactivity gradually disappeared in the months following transplantation. Five of 6 CSF samples from non-transplanted PD patients also produced this immunocytochemical reactivity whereas 26 non-PD samples were immunonegative. Possible implications to the transplant procedure are discussed.