Studies were carried out on the effects of different carbohydrates on the lysis of Trypanosoma cruzi, Trypanosoma rangeli and erythocytes caused by the bacteria Serratia marcescens variants SM 365 and RPH. High concentrations of d-mannose were found to protect T. cruzi and T. rangeli markedly diminishing the lysis caused by S. marcescens. However, this carbohydrate is unable to interfere with the hemolysis induced by SM 365 and RPH variants. These results showed that the trypanolytic effect induced by S. marcescens SM 365 and RPH variants is dependent on d-mannose and distinct from the hemolytic activity, strongly suggesting that bacterial fimbriae are relevant to S. marcescens in lysis of parasites.