Frequencies of all defined HLA-A, -B, -C (-DR) antigens were determined in 142 (59) Germans suffering from acute lymphoblastic leukemia (ALL) with differentiation of immunologically defined or age-related subgroups of the disease. A highly significant rise of the HLA-C locus antigen Cw7 was found in ALL patients, particularly those over the age of 11 in comparison with local German and Caucasian controls of the Ninth Int. Histocompatibility Workshop (WS). Only slight differences of HLA-Cw7 frequencies were observed within the four immunologically defined ALL subtypes of all or age-related patient groups. HLA-A, -B, or -DR antigens, as well as HLA-ABC three-locus haplotypes were similarly distributed in patients and their local or Caucasian controls. The results indicate HLA-linked genetic factors conferring susceptibility to ALL in adults, particularly those presenting with B-, T-, and Null-ALL.