The inhibiting effects of methylxanthines on urethan-induced lung tumors, malformations, and presumed somatic mutations in mice were studied to determine the contribution of mutational and physiological changes to chemically induced neoplasia and malformation. When young adult or pregnant ICR/Jc1 mice were treated with urethan and then methylxanthines were given, caffeine (1,3,7-trimethylxanthi...