Glycosylation mutants of chinese hamster ovary cells were used to analyse the role played by surface-exposed carbohydrates on the process of interaction of Trypanosoma cruzi with the host cell. Adhesion and invasion of the parasites were markedly reduced in cells which express very few sialic acid residues. Infection levels similar to those obtained with the parental cell could be obtained after sialylation of the mutant cell using exogenous fetuin as sialic acid donor and T. cruzi trans-sialidase. The results obtained show that host cell sialic acid residues are involved in the process of attachment to and penetration of T. cruzi into the host cell.