We studied the change in cytoplasmic free calcium ion concentration ([Ca2+]i) in the peripheral blood leukemic cells from adult T-cell leukemia (ATL) patients stimulated by anti-T3 (CD3) or anti-T11 (CD2) antibodies in order to see whether there is an abnormal response in the early activation processes following T3 or T11 antigen stimulation. Peripheral blood mononuclear cells (PBMC) from four T-cell chronic lymphocytic leukemia (T-CLL) patients showed a rapid and clear increase in [Ca2+]i (from 165 +/- 26 nM to more than 299 nM) when stimulated by OKT3 antibody and anti-mouse IgG antibody. This response was comparable to that of PBMC from 10 normal individuals (from 151 +/- 20 nM to 252 +/- 34 nM). In contrast, PBMC from 10 ATL patients showed only a slight increase in [Ca2+]i (from 137 +/- 21 nM to 176 +/- 32 nM) following T3 stimulation. The experiments with higher concentrations of OKT3 antibody suggested that this attenuated increase in [Ca2+]i in ATL cells was not exclusively due to impaired expression of T3 antigen. The [Ca2+]i increase in ATL cells induced by the stimulation with two anti-T11 antibodies recognizing different epitopes of the T11 antigen, however, was comparable to that of normal PBMC. The abnormal response of [Ca2+]i to the T-cell receptor/T3 antigen stimulation in ATL may be related to dysfunction or leukemogenesis of HTLV-I-infected cells.