Digestive disorders are very frequent in the course of immune deficiencies. Parasitic infestations are often their cause, Giardia lamblia was the first known agent and is chiefly found in deficiencies of humoral immunity. Recent studies allowed a better evaluation of the relationships between the host's immune system and parasite, such as production of anti-Giardia antibodies, presence of non specific anti-Giardia factors in blood and maternal milk and the part played by cellular immunity. Another protozoan of the cryptosporidium species was recently considered as responsible for severe diarrhea in cases with immune deficiencies, especially AIDS and some congenital immune deficiencies (5 cases in children with immune deficiencies and diarrhea during the past 3 years). Children without immune deficiencies may also be contaminated, as shown by several epidemiological studies. Finally, a third type of protozoan, Isospora belli and Isospora hominis was also involved in the occurrence of severe digestive disorders. All these parasitic infestations in children with immune deficiencies were characterized by their difficult treatment, their chronicity and frequent relapse and, overall by the usual association with other bacterial and viral agents.