Several T-lymphocyte clones obtained from rejected human kidney allografts and maintained for several months in recombinant IL2 and antigen-supplemented cultures were studied for their capacity to produce lymphokines in vitro. Six clones produced a factor able to increase 3HTdR uptake of the IL3-dependent DA-1 murine cell line. All were T4+, T3+ and T11+ and fitted with a probability of monoclonality above 97%. The factor, designated as human-interleukin-DA (HILDA), was not produced when autologous EBV-transformed B cells were added in the culture in the absence of exogenous IL2. Addition of pure recombinant IL2 along with donor EBV-transformed cell lines resulted in a sharp increase in HILDA yield, whereas a low amount of this factor was also produced with the autologous EBV B lymphocyte in the presence of exogenous IL2. Kinetics studies show that HILDA was detectable as early as 24 to 48 h, peaked at day 3 and plateaued until day 5. The antigen-exogenous IL2-driven pathway of HILDA production by clones was bypassed by use of either PMA or calcium ionophore (CaI) alone or associated in the culture. Both compounds induced dose-related HILDA production (without antigen and/or exogenous IL2). No synergistic effect of PMA and CaI was noted, although an additional effect could be seen when a suboptimal dose of CaI was used.