In a group of 74 adult ALL patients 25 had a transcortin level greater than or equal to 3 SD above the normal mean, 15 expressed an HLA-Cw3 antigen and 11 combined both characteristics. In this subgroup of 11 ALL patients, five had familial leukaemia, i.e. at least one relative with acute leukaemia or lymphoma. On the other hand, only three examples of familial leukaemia were found in a series of 59 ALL patients with one or none of these two characteristics (relative risk: 15.6; P less than 0.001).