Metaldehyde has been widely used as a main ingredient of solid fuel for making fire and slug baits in Japan. It is also marketed as a color flame tablet for party goods (ENGELFIRE). Consequently, children have been poisoned by eating such tablets which they mistook for candy. As a result, poison information center calls are increasing. According to POISINDEX, the treatment for metaldehyde poisoning consists in prevention of adsorption by activated charcoal, seizure control and airway protection. However, the optimum dose of charcoal is not established. We studied the quantitative adsorption capacity of activated charcoal for acute oral toxicity of metaldehyde in rats. In vivo toxicity and absorption tests for metaldehyde in Wister rats were done. The detoxifying effect of activated charcoal on metaldehyde toxicity and inhibition of metaldehyde absorption were investigated. Ratios used of po activated charcoal given 30 min after dosing to 400 mg metaldehyde/kg po were 5:1, 2:1, 1:1, 0.5:1. Serum metaldehyde was determined by gas chromatography in the control group (no charcoal) and the various experimental groups. Metaldehyde mortality was completely prevented at the ratio of 5:1. Gastrointestinal absorption of metaldehyde was reduced significantly by 45.3% in comparison to the control rats. There was no acetaldehyde detected in the serum of the metaldehyde-dosed rats. Metaldehyde poisoning may be prevented by early po administration of activated charcoal in a ratio of > 5:1 compared to metaldehyde. The theory that acetaldehyde is the primary toxic agent in metaldehyde poisoning should be re-evaluated.