Digestive apparatus is a common target of atypical mycobacteriosis in AIDS patients (at least 50% of patients with CD4+ lymphocytes < 50/mm3). We describe the clinical-histological features of two cases of Whipple-like syndrome likely caused by Mycobacterium avium (MAI) (study performed by light and electron microscopy), of one case of infection caused by two morphological variants of a MAI strain with a different sensitivity to antibiotics, of one case of M. kansasii infection and of two cases of M. genavense infection accompanied by sensitivity tests to antibiotics (as far as we know, these are the first described quantitative sensitivity tests of M. genavense to antibiotics). In conclusion, we discuss the present therapeutical outlines for M. kansasii and avium, together with the teramporary pharmacological options for M. genavense as suggested by antibiotic sensitivity tests performed on the strains isolated from the studied patients.