Probing a cerebellar expression library with TrAb sera from patients with Hodgkin's disease and paraneoplastic cerebellar degeneration resulted in the isolation of MAZ (myc-associated zinc-finger protein). Eleven of 19 TrAb sera and 16 of 131 controls reacted with MAZ, indicating a significant, although not specific, association between Tr and MAZ immunities (p < 0.001). Interestingly, 9 of 16 positive control patients also had cerebellar dysfunction. Purified MAZ antibodies reacted with Purkinje cells. In neuronal cells, MAZ interacts with DCC (Deleted in Colorectal Cancer product), the receptor for netrin-1, a neuronal survival factor. These findings suggest epitope spreading between the Tr antigen and the MAZ-DCC complex and offer a possible model of immune-mediated cerebellar disease.