HLA antigen typing was carried out in a family with an autosomal dominant form of spinocerebellar degeneration [possibly olivoponto cerebellar atrophy (O.P.C.A.) — Type 1] . Eleven ataxic patients, three possibly ataxic subjects, two unrelated spouses and 13 clinically normal at risk siblings were typed for ABO and Rh blood groups, HLA-A and HLA-B antigens, C4 component of the complement and a number of other serum proteins (Clq, (β -1A, (β-1C, C5, (β -lipoproteins). No solid evidence for linkage between the ataxia gene and the HLA or C4 loci could be demonstrated in this family. Certain serum proteins, and particularly β -lipoproteins were found to be significantly reduced in some sub-groups of subjects.