The carcinogenicity of a potent mutagen, 1,6-dinitropyrene (1,6-DNP), was examined by intratracheal instillation into non-inbred Syrian golden hamsters of both sexes. Animals were treated with 0.5 mg of 1,6-DNP suspended in 0.2 ml of saline intratracheally once a week for 26 wk. Lung carciomas developed in experiemntal weeks 20-48 in 100% and 90%, respectively, of the male and female hamsters treated with 1,6-DNP. Besides lung carcinomas, myloid leukemias developed in 60% of both males and females treated with 1,6-DNP. No tumors were found in control hamsters.