The prognostic significance of immunophenotypical properties of leukaemic cells is well known. However, the biological and clinical significance of CD7 and CD56 antigen expression in acute leukaemias are not clearly established. In patients with acute leukaemias, we identified CD7 and CD56 expression and analysed their associations with markers expressed early in haemopoietic ontogeny and clinical parameters. Among 22 patients with acute leukaemia [12 acute myeloblastic leukaemia (AML), 10 acute lymphoblastic leukaemia (ALL)], we found CD7 positivity in 15 of 22 patients (68%) and CD56 positivity in four patients (18%). CD7 positivity was observed in seven patients (58%) with AML and in eight patients (80%) with ALL. CD56 positivity was observed in three patients (25%) with AML and one patient (10%) with ALL. Lymphadenopathy was present in five patients and associated with hepatosplenomegaly in three patients with ALL. Splenomegaly and hepatomegaly were present in three patients with AML. Central nervous system involvement was seen in one patient with ALL. Complete remission was achieved in nine patients (41%) (five ALL and four AML). Our data showed that CD7 and CD56 positivity at diagnosis associated with low remission rate and biological aggressiveness in a significant proportion of patients. We suggest the evaluation of CD7 and CD56 in all patients with acute leukaemias at the time of diagnosis in view of poor clinical outcome.