In order to determine characteristics of Blastocystis (B.) hominis infection; 770 individuals' stool specimens were examined both by simple and concentration techniques and stained with iodine solution and trichrome in the Parasitology Laboratory of Hacettepe University Faculty of Medicine, Turkey. Among the examined 770 specimens, B. hominis was detected in 94 (12.2%). B. hominis was the most common intestinal parasite among the study group. It was mostly detected with Dientamoeba fragilis. Among the groups the incidence of B. hominis in allergic patients was higher than controls. Among the immunosuppressed patients, B. hominis was detected significantly higher in patients who had solid tumours. Of the 48 individuals who had only B. hominis in their stool the most common symptom was abdominal pain. Concentration technique with trichrome stain was more sensitive than simple smear with lugol solution for the detection of B. hominis. Studies with more patients must be planed to understand the B. hominis infection in solid tumour patients and coexistence of B. hominis and D. fragilis.