Standards are lacking for validation of drug causality assessment methods. An original model is proposed using a positive rechallenge as an external standard. This model was used to validate the novel causality assessment method (RUCAM) described in the previous article (Part I; J Clin Epidemiol 1993; 46: 1323). Seventy seven reports of drug-induced acute liver injuries with positive rechallenge were collected from the medical literature and divided into 49 cases and 28 controls. The RUCAM was applied to information obtained prior to readministration. The score was significantly higher (p < 10(-4)) in cases than in controls with high levels of sensitivity, specificity and predictive values. It is concluded that (1) adverse drug reaction reports with a positive rechallenge can provide a standard for validation of causality assessment methods, (2) RUCAM applied to drug-induced liver injuries has been validated.