One hundred thirty-two cases of severe acetaminophen (paracetamol) poisoning were treated with oral methionine. Seven of 96 patients who received the antidote within ten hours of ingestion of the overdose had severe liver damage (aspartate transaminase level, greater than 1,000 IU/L), but none of these patients died. Thirty-six patients received methionine between ten and 24 hours of ingestion; severe liver damage occurred in 47%, and two patients died. The treatment protocol for oral methionine is simple, and therapy is complete within 12 hours as compared with three days for oral acetylcysteine and 20 hours for intravenous acetylcysteine. Side effects from methionine were unimportant. Oral methionine is as effective as acetylcysteine in preventing severe liver damage and death after acetaminophen overdose. However, as with acetylcysteine, it must be given within ten hours of ingestion to be effective.