Feces of 798 male and female patients who attended the Parasitology Laboratory of the "Facultad de Ciencias Bioquímicas y Farmacéuticas de la Universidad Nacional de Rosario (República Argentina)" were examined. Out of the total number of samples, 281 were collected after a purgative, and 517 by serial collection. The samples were examined applying the routine parasitological analysis. Those which presented Blastocysts hominis were processed for their quantification and classification in different categories according to the number of cells per microscopic field with a magnification of 400 x. B. hominis appeared in 25.2% of the patients. Practically the same percentage was detected with either collection method. B. hominis was associated with other parasites, appearing as the only parasite in only 29.4% of the cases. Both its statistical association with the patient's age and its independence from sex were determined. The most frequent symptomatology in patients with B. hominis only was: abdominal pains, pruritus, flatulence, malaise, anorexia and diarrhea. Only 14.9% did not present any symptoms at all. The search for this protozoa should be a parasitological routine analysis since it is the cause of frequent intestinal disorders.