Since 1986 we have been observing an increased number of patients with megaloblastic anaemia (MA) associated to chronic diarrhea. In 60% of the cases we could not identify any etiologic factor. In the last three years a prospective study in Lima (Peru) has been carried on aimed to investigate this aspect; patients with diseases recognized to be associated to MA were excluded. 45 patients were included age average 37.5 years, all of them have a confirmed diagnosis by bone marrow; 64% with low serum B12 and folic acid, 20% with low serum B12, and 16% with low serum folic acid. Gastric biopsies did not show atrophy in 67%; intragastric pH was lower than 4 in 50% duodenal content culture was positive in 35% (6/17) to aerobic gram negative agents; 62% (5/8) of duodenal biopsies, 83% (5/6) of jejunal biopsies, 4/4 (100%) of ileal biopsies, showed diverse structural changes; 100% did not show Diphyllobothrium pacificum. All these findings make us suggest that a significative number of patients with MA and chronic diarrhea in Lima are related to small bowel bacterial overgrowth. These bacteria can "sequestrate" or consume folates and cobalamines besides the direct damage they can cause to intestinal morphology. Future studies are needed to confirm our proposal and define if these cases belong to a variety of tropical sprue.