Aflatoxins are one of the most potent toxic, mutagenic, teratogenic, cancerogenic, and immunosuppresive substances that naturally occurring contaminants of food. There are some studies in various animal species that have reported aflatoxin effects on gastrointestinal systems, but acute effects of aflatoxins have not been clearly investigated. In this study, we aimed to investigate the acute gastrointestinal effects of total aflatoxin on rat isolated proximal and distal colon. Aflatoxin was given cumulatively at 10(-8)-10(-5)M concentrations and the amplitude and frequency of proximal and distal colon contractions were increased significantly. In the presence of atropine sulfate (23.6 nM) and morphine (0.3 microM) the amplitude and frequency of aflatoxin induced spontan contractions in the proximal and distal colon decreased significantly, on the other hand, L-NNA (0.3 microM) increased contractions' amplitude and frequency significantly in the proximal colon but not in the distal colon. In conclusion, aflatoxin may increase the amplitude and frequency of contractions by increasing muscarinic activity or by decreasing NO synthase and/or release in proximal colon and by increasing muscarinic activity in the distal colon. These findings of aflatoxin on isolated rat proximal and distal colon may explain their acute gastrointestinal effects in humans and animals.