Human infection is the result of a complex interplay of factors pertaining to the invading organism, the host, and the environment. This is best shown in human dermatophyte infections. Acute infections are usually short-lived and easy to treat. The patient has good cell-mediated immunity, short-term antidermatophyte antibodies, and delayed hypersensitivity. In chronic infections, the infection is long-term and resistant to therapy. Patients have poor in vitro assessed cell-mediated immunity and immediate hypersensitivity to fungal antigens. Antidermatophyte antibodies usually do not disappear quickly. Development of more specific and sensitive assays will add to our understanding of this unique host-parasite relationship. The speculative role of anti-idiotypic antibodies is discussed.