244 male infants were admitted for studies on dietary therapy of acute diarrhea. All patients had complete history and physical exams, anthropometrics, and extensive laboratory tests, including stool studies for virus, bacteria and parasites and metabolic balance studies. Rehydration and replacement of ongoing losses were carried out following WHO guidelines. Feeding was started after 4-8 hours rehydration. Antibiotics were given for proven Shigella or Campylobacter. Giardia was treated on day 7. Treatment failures defined as recurrence of dehydration, and severe or prolonged diarrhea, were treated individually. Patients were grouped by etiological agent to compare initial presentation and clinical and nutritional outcomes. Covariance analysis was used to correct the effect of confounding variables not associated to etiology; then discrete and continuous variables were compared by chi square and ANOVA, respectively. Patients were divided in 6 groups: ETEC: 31(13%), EPEC: 29(12%), RV: 23(9%), other bacteria: 24(10%), mixed infections: 70(29%) and no pathogens: 67 (27%). Diarrhea duration before admission was longer in the EPEC group and shorter in RV patients, who also had more vomiting, dehydration and acidosis. There were no differences in frequency of failures according to etiology. Diarrhea duration was shorter for the RV group and longer with the ETEC group. Stool output was higher for the RV and mixed groups and lower for the “none” group on the first 2 days. Likewise, nitrogen, fat, carbohydrate and energy absorption and nitrogen retention were lower for the RV, other, and mixed groups during the first 2 days. Begining on day 3 there were no differences among the etiological groups regarding stool volume and nutrient absorption. Neither there were differences regarding changes in weight, skin fold thickness or serum albumin, from day 1 to day 7. Conversely, weight and skin folds increments correlated strongly with total energy intake.