Signalling through CD30 has been shown to mediate pleiotropic effects, depending on the type of target cell. In the present study, we have used the agonistic anti-CD30 monoclonal antibodies (MoAb) M44 to study phenotypic changes in human T-cell clones of Th1 and Th2 type. Alterations in the surface expression of CD30, CD28 and CD40L following CD30 stimulation were analyzed after 24 h, and the cytokine production after CD30 crosslinking was measured at 48 h. We observed a clear reduction of surface expression of CD30 after treatment with the M44 MoAb. Our results also indicate that CD28 is significantly down modulated in the Th2 clones after CD30 crosslinking (P < 0.05, n = 5) whereas no apparent alteration was observed in the expression of CD40L. When the concentration of cytokines was measured in the supernatants after CD30 stimulation, elevated levels of interleukin (IL)-4 and IL-5 were observed in the Th2 clones, and elevated levels of interferon (IFN)-gamma in the Th1 clones. The enhanced cytokine production after CD30 crosslinking supports the presumption of CD30 functions as a positive regulator in activated T cells.