It was recently reported that IL-10 is protective in Acetaminophen (APAP) toxicity and it down-regulates iNOS production. In an ongoing Pediatric Pharmacology Research Unit (PPRU) Network study, plasma IL-10 levels were higher in patients that developed significant toxicity, as compared to those with minimal hepatic transaminase elevations. In these patients IL-10 elevation is likely a compensatory response to hepatic injury. To further examine the relationship of IL-10 and iNOS in the APAP overdose patients, we will examine genetic variability in the promotor regions of iNOS and IL-10 in patients with APAP overdose. Data from the literature indicate the polymorphisms in the promotor regions of iNOS and IL-10 influence the severity and expression of various diseases. In addition to genotyping for iNOS and IL10 promotor region polymorphisms, plasma levels of nitrotyrosine and IL-10 will be measured in overdose patients.