To identify the efficacy and tolerance of activated charcoal in acute, nonspecific diarrhea.Randomized, double-blind study on 100 adults with nonspecific diarrhea, performed in two general practices. 94 were included in the final analysis, 6 patients - all from the placebo group abandoned treatment because of the absence of an effect.The major outcome parameters - reduction of stool frequency and curtailment of the duration of the diarrhea - were unequivocally achieved. Differences between the agent and placebo were great. Stool frequency decreased significantly from the third day in the drug group, and highly significantly from the fourth day. The superiority of the antidiarrheal was also clearly evident in terms of the numbers of days with diarrhea, the clinical findings tympania, nature of the stool and of eight individual symptoms, the summed score of which was improved highly significantly by the test substance.The substance tested proved rapidly and reliably effective in the treatment of nonspecific diarrhea, and was well tolerated. Activated charcoal, together with oral rehydration, can therefore be recommended as an initial measure for treating diarrhea with the aim of rapidly and effectively preventing loss of fluid and electrolytes and relieving symptoms.