1. Human leucocyte ABC antigens were determined by means of a lymphocytotoxicity test in 27 patients with previous essential malignant hypertension and in 500 blood donors.
2. In 18 patients with grade IV retinopathy human leucocyte antigen B15 (HLA B15) was found in 44%, as compared with 23% in the control subjects (P = 0.888).
3. All patients with HLA B15 had a positive family history for hypertension.
4. In 18 patients with grade IV retinopathy HLA B15 was found in eight whereas none of the nine patients with grade III retinopathy had this antigen (P = 0.039).
5. Of the 27 patients, 19 had a positive family history of hypertension and of these eight had HLA B15, whereas none of the eight patients with a negative family history had this antigen (P = 0.068).
6. The findings do not rule out that HLA B15 may be associated with the development of the malignant phase in patients with essential hypertension, but a statistically significant relationship could not be established.