The goal of these studies is to increase understanding of the pathogenesis, and to improve diagnostic and therapeutic measures for parasitic diseases. A method of purifying bovine cryptosporidial oocysts for use as an antigen in an ELISA test was developed. IgM and IgG antibody responses were demonstrated in immunocompetent as well as in AIDS patients, with indications the Cryptosporidium is a common human infection. The criteria and specificity for an immediate hypersensitivity skin test for stronglyloidiasis have been established. For immunodiagnosis of filarial infections efforts to improve the sensitivity assays for circulating filarial antigens are continuing. Therapeutic trials underway include a double-blind prophylactic trial of DEC against acquisition of Loa loa infection in Peace Corps volunteers in Africa, treatment of cerebral cysticercosis with praziquantel, treatment of strongyloidosis with Ivermectin, and use of ivermectin to treat lymphatic filariasis in India. Recombinant gamma interferon was found to show limited effects in treating anergic cutaneous leishmaniasis. The relationship of the immune response to immunopathology in several types of helminthic and protozoan infection is being examined. The antigen-specific T-cell suppression in filariasis and leishmaniasis was demonstrated to be at the level of lymphokine (IL-2 and gamma-interferon) production. The relationship between IgE and IgG4 generating and inhibiting allergic responses to parasites was aided by the use of anti-subclass monoclonal antibodies. Broncho-pulmonary lavage revealed persisting alveolitis in tropical pulmonary eosinophilia patients after therapy, suggesting that more intensive treatment may be necessary. Giardia isolates from various sources are being characterized as to their DNA composition, surface antigens and biologic behavior. Several isolates will be used for human volunteer infections.