A set of eight rapid laboratory test were used to study 100 fecal samples from children with acute diarrhea (Leucocytes, blood, reduced sugars, pH, modified gram stain for Campylobacter, Ziehi-Neelsen for Cryptosporidium, and Rotavirus latex). Specific therapy plus standard rehydration therapy was given according to the etiological agent. A control group was studied doing common laboratory test such as fresh examination of the stool to define the presence of parasites and leucocytes. Defining enteritis or entercolitis and the etiological agent by using rapid laboratory test, allowed a specific therapy and the reduction of the number of days with clinical disease, as compare with the control group. Fecal leucocyte count done in fresh examination with methylene blue (5 cells predominantly neutrophils per high power field), was the more useful test to define a disease caused by invasive pathogens. In the control group 2 ++ or more of leucocytes at fresh examination showed a good correlation with prolonged diarrhea (7 to 15 days). According to the results a flow chart for the correct study and treatment of acute dlarrhoea dlsease in chlldren is suggested.