N-Acetyl-p-aminophenol (acetaminophen) is one of the main metabolites of acetophenetidine (phenacetin), which was proved to be a carcinogen. Ishidate and Odashima have found that acetaminophen itself induced chromosomal aberrations in cultured Chinese hamster cells. The repair test by the rec-assay also gave a positive result (Kada et al., unpublished data). These results prompted us to perform an experiment of long-term administration of acetaminophen in B6C3F1 mice.
During the preparation of this article Flaks and Flaks have reported that acetaminophen is tumorigenic in mice of the IF strain. The difference between results of the present study and the results obtained by Flaks and Flaks is briefly discussed.