In the last few years, some surface molecules which preferentially associate with human Th1 or Th2 cells have been described. Th1-related molecules include CD26, membrane IFN-gamma, LAG-3, CCR5 and CXCR3, whereas CD62L, CD30, CCR3, CCR4, CCR8, and in a certain way even CXCR4, preferentially associate with human Th2 cells during certain phases of their differentiation/activation process. Although none of these molecules can be considered as a truly selective marker of human Th1 or Th2 cells, their combined detection may help to characterize the pathway of the specific immune response both in vitro and in vivo. Moreover, the understanding of mechanisms responsible for these associations may provide new insights into the functional programs of the specific effector cells, as well as on their regulation.