In developing countries where helminth infections are highly prevalent, Th1 autoimmune diseases are almost never reported. A hypothesis suggesting that this may be due to effects of helminth infection on the immune system has been developed, and has inspired scientists to explore the possibility of using helminth antigens to treat autoimmune diseases. In animal models, helminth infection and helminth products have been successfully used to prevent different Th1-mediated autoimmune diseases. Results from initial studies were interpreted based upon the Th1/Th2 paradigm: A Th2-polarizing helminth infection correcting a Th1 autoimmune 'imbalance'. Intriguingly, however, allergies rarely develop in the host, despite the strong Th2 polarization induced by parasite antigens. Helminth infections act on the immune system of the host at many different levels. For this reason, identifying one or more products with therapeutic potential, from the 20,000 genes that a helminth can express, is a challenging task. In this review, we summarize the results achieved in animal models, and suggest possible approaches for the design of therapies appropriate for use in human Th1-mediated autoimmune pathologies.