Between 2002 and 2003 the Authors analyzed stool specimens of 1,989 subjects, 966 children (1-14 years old) and 1,023 adults, to investigate for intestinal protozoa too: 380 children and 656 adults with intestinal aspecific troubles, 546 children and 291 adults with acute diarrhoea, 40 children and 76 adults with prolonged diarrhoea. G. duodenalis prevailed in 1.8% of all cases (0.2% among children and 3.2% among adults), D. fragilis in 4.1% (0.6% and 7.3% respectively). Other pathogenic parasites were very rare. Only B. hominis (opportunistic/saprophytic protozoon) or other commensal protozoa were observed, also associated with D. fragilis and/or G. duodenalis. Among subjects suffering from intestinal aspecific troubles, G. duodenalis prevailed in 3.7% and D. fragilis in 8.7% of adults; both protozoa were observed in 0.5% of children each one. Among acute diarrhoeas G. duodenalis was observed in 1.7% of adults and never in children, D. fragilis in 4.5% and 0.4% respectively. Among prolonged diarrhoeas, G. duodenalis was observed in 5.3% of adults and never in children, D. fragilis in 6.6% of adults an in 5.0% of children. The Authors emphatyze the clinical importance of D. fragilis and the diagnostical importance of a permanent stain, like Giemsa, for a good and sure diagnosis.