Rats inoculated with Trypanosoma cruzi were divided into two groups maintained, respectively, on a low and a rich protein diet. Ninety-eight days after inoculation the cardiac levels of noradrenalin in the well-nourished infected rats were not different from those of uninfected controls. In the malnourished group, however, these levels were around 50% of the control values. In addition, the adrenergic nerve terminals were clearly reduced in the auricular appendages of 87.5% of the malnourished infected rats. These results indicate that protein deficiency at least delays the recovery of noradrenalin levels that normally occurs during the chronic phase of experimental Chagas' disease.