Entamoeba histolytica trophozoites are able to degrade human erythrocytes; the loss of erythrocyte cellular matrix and degradation of plasma membrane were observed, along with the decrease in the average size of digestive vacuoles. Ninety-six percent of hemoglobin ingested was hydrolyzed by trophozoites within 3h, as evidenced by electrophoresis. Accordingly, X-ray spectroscopy revealed the presence of iron inside vacuoles after erythrophagocytosis, the concentration of which decreased to control levels in a similar period. Quantification of erythrocyte digestion at the early and late periods was determined by a spectrophotometric procedure, with t(1/2)=1.67 h and 35-min for HM-1:IMSS and HK-9:NIH trophozoites, respectively. In the latter, activity was due to the combined action of intracellular enzymatic activity and exocytosis. E-64c and leupeptin totally inhibited erythrocyte digestion within a 3-h period, thereafter hydrolysis took place at lower rate. Our results suggest that erythrocyte digestion in E. histolytica proceeds in different ways in these two amebic strains, and can be blocked by proteinase inhibitors.