Leukemic cell expression and serum levels of CD4, CD8, and interleukin-2 receptor (IL-2R) were determined at diagnosis for children or adolescents with acute myeloid leukemia (AML). Cellular expression of CD4 was detected in 18 of 62 cases, CD8 in none of 60 cases, and IL-2R in one of 33 cases tested. Myeloblasts of the M4 and M5 subtypes expressed CD4 significantly more frequently than other FAB subtypes (p = 0.0001). Serum levels of the three soluble factors (tested for 91 patients) were positively correlated with each other. Increased serum CD4 levels were significantly associated with cellular CD4 expression, high leukocyte count, M5 leukemia, spleen enlargement, and age less than 1 year. High serum CD8 levels correlated significantly with splenomegaly, extramedullary disease, absence of Auer rods, and high leukocyte count. Cases with high serum IL-2R levels were less likely to have Auer rods and more likely to have splenomegaly and M5 leukemia; serum levels greater than 750 U/ml were associated with a higher probability of treatment failure (p = 0.05), even after adjustment for other potential prognostic factors. Further studies of serum CD4, CD8, and IL-2R levels may help to clarify the immunoregulatory role of T-cells in patients with AML.