Eighty-three patients with B cell chronic lymphocytic leukaemia were typed for HLA-A,B, and DR antigens. HLA-A2 was found to be significantly increased in patients compared to controls. The frequency of antigens A2,B12(44),DR7 occurring together was more than double the frequency found in the controls. In 48 patients requiring treatment, there was a significant reduction of B8 when compared to 34 untreated patients, and DR7 was significantly increased in frequency in treated patients. Thirty patients presented with sub-clinical symptoms (Rai stage 0). HLA-A10 was significantly more common than in those patients presenting with more advanced disease (Rai stages 1-4). The highest frequency of any HLA antigen was found in males presenting with clinical symptoms, 71.0 per cent of whom were A2 positive; in the same group, 22.6 per cent of patients were positive for all the antigens A2,B12(44),DR7. Patients with an age of onset greater than the mean age of 69 years were more likely to be A2 positive. We conclude that HLA-B8 is a marker of mild disease while HLA-A2 and the closely associated antigens B12(44) and DR7 are markers for severe disease.