The autoimmune response to mouse accessory glands (MAG) was investigated in male BALB/c mice immunized with different doses of chemically modified mouse accessory glands (MMAG) and complete Freund's adjuvant (CFA). This autoimmune response was studied at several time intervals using the skin test with MAG. It was found that 5 mg of MMAG induced on the day 15 an autoimmune response detected by specific skin test at 20min., 3h and 24 h. The results of the immediate type hypersensitivity (ITH) were higher than those with the other skin tests. In order to study the type of immunoglobulin involved, the ITH was also analyzed by passive cutaneous anaphylaxis (PCA) at different time intervals with treated and untreated sera at 56°C. The findings suggest the presence of reaginic antibodies, IgE being the major antibody as detected by enzime linked immunosorbent asay (ELISA).The MAG was subsequently fractionated using Sephandex G-100 and the fractions thus obtained (FI. FII and Fill) were used to challenge mice immunized with MMAG. It was found that FI was the only fraction which revealed an ITH similar to that revealed by MAGThe effect of infection withTrypanosoma cruzion the autoimmune response to MAG was analyzed with different mouse groups intraperitoneally treated with 2×103blood trypomastigotes/animal at several time intervals: namely, on days−5, 0, +5 and + 10 with respect to the immunization with MMAG. The autoimmune response to MAG showed suppression when the animals received the parasites on the same day as the autoantigen.