The aim of our study was to ascertain whether granular cell degeneration represents uniquely an artifiactual or a supravital event in patients with oat cell carcinoma. The material includes 52 cases of small cell lung cancer (SLC). formalin fixed and paraffin embedded representative cerebellar slides were stained routinely (HE, Kluver-Barrera), and some of them served as material for immunohistochemical study. The following antibodies were used? anti-ferritin, anti-GFAP, anti-IgG and anti-C3 complement fraction. Finally 5 cases out of our material could be diagnosed as paraneoplastic cerebellar degeneration (PCD). on the basis of lack of metastases within the CNS and concomitant intensive loss of Purkinje and granule cells. Clinically the cerebellar syndrome was disclosed in 3 cases. In the granular layer prevalence of microglial cell reaction was noted. GFAP-labeled astroglia were not demonstrated in the same intensity. Antisera to the C3 complement fraction showed moderate staining of Purkinje cell cytoplasm and in 4 cases also in granule cell nuclei. The immunopathological changes presently observed and glial cell proliferation could be evidence for a nonartifactual origin of PCD.