Patients with HIV infection often suffer from opportunistic and bacterial infections of the digestive tract. The most common agents are Candida albicans, Herpes simplex and Cytomegalovirus, Mycobacterium avium intracellulare, Cryptosporidium parvum, and enteropathogenic bacteria such as Salmonella, Shigella and Campylobacter. The diagnosis is established by means of microbiological examination of blood and faeces, often supplemented by gastrointestinal endoscopy, with mucosal biopsies for culture and histology. Most patients respond well to specific treatment, but the infections tend to relapse after withdrawal of drugs.