Chagas¡¦ disease induced by Trypanosoma cruzi infection causes damages in heart and digestive tract of the host, but trypanosomes were rarely found in blood and tissue during chronic infection. Although trypanosomes could not be found in the peripheral blood of Trypanosoma musculi infected mice during chronic stage, trypanosomes detected in vasa recta of kidney became a unique kidney form (KF). In this investigation, BALB/c mouse was used as animal model to examine if kidney form of T. cruzi exists in chronic stage. Kidney sections were made on the 20, 40, 60, and 80th day after infection of each mouse with 1,000 bloodstream trypanosomes. In order to compare with chronic stage, kidney sections obtained from mice 20 and 40 days after infection were regarded as acute phase. Amastigotes of T. cruzi as well as significant tissue damages were found in both acute and chronic stages. The results indicated that T. cruzi may exist in amastigote form in mouse kidney during chronic infection. ELISA was employed to measure mouse serum specific antibody titers which recognize mouse kidney antigen infected with trypanosomes 20 to 300 days respectively. Peak titer was observed on the 40th day of infection. Results showed that the ability of acute serum recognizing infected kidney antigen was better than chronic serum. On the other hand, antibody titers that recognize amastigote antigens increased gradually during the infection. It seems correlated with trypanosomes existing and releasing antigen during chronic infection. Antisera from rat immunized with epimastigote or amastigote could recognize infected and normal mouse kidney antigen. Anti-epimastigote sera detected 27 and 49 kDa proteins and anti-amamastigote sera detected 28 and 48 kDa proteins of infected mouse kidney antigen. Functions of these molecules are still not clear and require further characterization in the future.