The aim of the present work was to investigate malabsorption associated with Strongyloidiasis. Two groups were studied, one composed of 40 patients in which larvae were found either in the stools or in the duodenal aspirate, and a control group of 15 normal (negative stools and duodenal aspirates and absence of any other conditions leading to malabsorption). Both groups were hospitalised and studied from the clinicai (changes of intestinal rythm, dyspepsia, food intolerance, epigastric pain, weigth loss, etc.), laboratorial (fecal fat estimation in 5 day periods, d-xilose excretion, blood carotene leveis, lactose tolerance tests, etc.) and radiological standpoint (transit time, investigation for evidence of hypersecretion, floculation, puddling, segmentation). Biopsy specimens were scrutmized for congestion, edema, broadening and/or shortening of the villi. Patients were divided in sub-groups according to the foregoing parameters, in an attempt to correlate the clinicai and laboratory data with radiologic and histopathologic findings. The average fecal fat excretion in normais was 3.1 g/24 hs, while 24 patients (60%) excreted more than 5.5 g/ 24 hs, and 10 patients had overt steatorrhoea more than 10 g/24 hs. A significant correlation was the finding of higher leveis of fecal fat in patients with morphological changes of the small bowel, pointing to the fecal fat as the most reliable index of malabsorption, whereas the other tests gave inconsistent results in the different groups. The histological and radiological abnormalities were always present in patients with steatorrhoea, varying from minimal to the most severe changes.