The high sensitivity that can be attained using an immunoassays coupled to a rotating bioreactor with electrochemical detection mediated by [Os(bpy)2Cl(pyCOOH)]Cl, has been verified for the detection of Trypanozoma cruzi (T. cruzi), This protozoan parasite causes Chagas disease, affecting more than 18 million people in central and south America. Antibodies in the serum sample are allowed to react immunologically with whole homogenates of the parasite as antigen that are immobilized on a rotating disk. The bound antibodies are quantified by a horseradish peroxidase (HRP) enzyme labeled second antibodies specific to human IgG in presence of hydrogen peroxide using an osmium complex [Os(bpy)2Cl(pyCOOH)]Cl as enzymatic mediators. The amperometric measurement performed at 0.00 V versus Ag/AgCl can be done within 2 min and the analysis time does not exceed 23 min. The calculated detection limits was 0.01 mIU ml(-1). Reproducibility assays were made using repetitive serum of 0.182 mIU ml(-1) T. cruzi specific antibody (measured as the activity of the correspondent anti-serum's enzyme conjugated); the percentage standard error was less than 5%. The amperometric immunoreactors showed significantly higher sensitivity and lower time consumed than the standard spectrophotometric detection ELISA method.