The possible association of 7 HLA specificities in the HLA-A locus and 16 specificities in the HLA-B locus with susceptibility to Parkinsonian syndrome was investigated in a total of 36 patients with paralysis agitans (PA), as well as in 11 patients with other Parkinsonian syndromes, and 176 controls in Japan. There was no clear association between HLA-A or -B locus antigens and PA or other Parkinsonian syndromes. Patients with PA were subdivided according to sex, age of onset, clinical manifestations, and response to L-Dopa therapy. There was, however, no apparent association between HLA-A or -B locus antigens and any of the variables investigated. Our data do not provide any evidence for genetic susceptibility in the pathogenesis of PA.