Clinical and biological features were assessed in 114 consecutive previously untreated adult acute myeloid leukaemia (AML) patients whose diagnosis was based on FAB criteria and detailed immunophenotyping. All patients received standard intensive chemotherapy. The main purpose of this study was to establish the prognostic value, if any, of terminal transferase (TdT) expression in myeloid leukaemia. TdT positive cells (7-80% of total blast cells) were detected in 40% of the cases. Among clinical characteristics, a low lactate dehydrogenase (LDH) (less than 250 I.U.) (P = 0.003), a low initial white blood cell count (less than 10 x 10(9)/l) (P = 0.002), and an absolute neutrophil count (less than 5 x 10(9)/l) (P = 0.02) were associated with TdT-positivity. FAB classification was not predictive of TdT expression, and there was no difference in the distribution of FAB subtypes between the groups. Multivariate analysis combining clinical and laboratory data indicated that a low expression of the monocytic antigen CD14 was predictive of TdT positivity in AML (P = 0.01). Karyotyping showed no difference in the pattern of occurrence of specific abnormalities between the TdT+ and the TdT- group. When clinical and immunophenotype data were included in a prognostic model, the patient's age was highly predictive of response (P less than 0.001), and only the CDw65 antigen contributed to the response model (P = 0.07). TdT+ patients with a low expression of CD11b achieved a higher frequency of response at a borderline level of significance (P = 0.06). Frequency of response to chemotherapy, the response duration or overall survival were not influenced by TdT expression.