HLA antigens were determined in 50 patients with hyperostotic spondylosis (Forestier's disease), and compared with 1244 normal controls. There was no significant difference in the distribution of HLA B27 between the two groups. However, there was an increased incidence of HLA B8 among the patients with hyperostotic spondylosis (42 per cent), as compared to the normal controls (17.5 per cent). This difference was statistically significant (p less than 0.005). Sixteen of the 50 patients with hyperostotic spondylosis had evidence of diabetes mellitus, 12 of whom also had the HLA B8 antigen. Thus patients with hyperostotic spondylosis have an increased incidence of HLA B8, associated with an increased incidence of diabetes mellitus.