We evaluated the in-vitro interaction of normal human eosinophil leucocytes and a virulent strain of Entamoeba histolytica (HM1-IMSS) in the presence of immune serum. At a 10:1 (eosinophil:amoeba) ratio a significant time-dependent destruction of eosinophils was found from the first hour onward, and a similar, albeit weaker, cytopathic effect was found in the 200:1 ratio mixtures, with some delay in the microscopic evidence of such effect. Results were unaffected by serum factors, and amoebae emerged virtually unharmed throughout these experiments, again regardless of the presence of serum factors. These results indicate that, as with neutrophil leucocytes, virulent E. histolytica is capable of destroying normal human eosinophils in vitro.