Summary.This study is intended to establish biological correlation between the expression of lymphoid associated features in acute myeloid leukaemia (AML). In 62 AML patients, predominantly enrolled on Eastern Cooperative Oncology Group (ECOG) treatment protocols, in whom immunoglobulin (Ig) as well as T‐cell receptor beta chain (TCR‐beta) gene rearrangement analyses had been performed, morphology, cytochemistry, antigen profile and karyotype were reviewed retrospectively. Nuclear reactivity with anti‐TdT antibody was demonstrated in 34 patients (55) and confirmed by ribonuclease protection assay in all patients tested. Five TdT‐protein negative patients were TdT‐transcript positive. Lymphoid antigens (lyA) were detected in 24 of 51 cases tested (47) with B‐cell antigens (CD19. CD10) being restricted to TdT+AML (P= 0.03). Only two patients had Ig heavy, none had Ig light chain or TCR‐beta gene rearrangements. Although both patients with rearranged Ig loci were TdT+, either by protein or RNA analysis, the low incidence of such rearrangement within the TdT* AML group (6) argues against a significant association between the presence of TdT and crosslineage Ig gene rearrangements in AML. While FAB‐diagnoses did not differ between TdT+ and TdT or lyA+and lyA−AML, particular immunophenotypic features correlated with TdT positively, e.g. the presence of early antigens, CD34 and HLA‐DR, and the absence of the more mature myelo‐monocytic antigens, CDw65 and CD14. Certain cytogenetic abnormalities were associated with TdT+AML such as inv(16) (p13q22) or t(16:16) (p12;q22) (five patients;P= 0.03) and t(8;21) (q22;q22) (three patients). A greater number of TdT−than TdT*AML patients had only normal karyotypes (P= 0.06). Neither immunophenotypic nor karyotypic correlations could be
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