Transmission of site-specific tumorigenicity (papillomas in larynx and trachea) of diethylnitrosamine (DEN) to the 2 subsequent generations (F1 and F2) was studied using an outbred strain (Han:AURA) of pregnant Syrian golden hamsters (P generation), which were treated i.p. with 10 mg/kg b.w. of DEN on day 12, 13 or 14 of gestation. Laryngotracheal papillomas were induced by DEN in the P and F1 generations only, while these tumours did not occur in the F2 generation. Spontaneously occurring tumours, including uterine adenocarcinomas, lymphomas, and laryngotracheal neuro-endocrine cell tumours, were observed at higher incidences among the F2 animals derived from the P generation hamsters treated with DEN only on day 13 or 14 of gestation. In the same animals, the ratio of malignant to benign tumours was considerably higher than in controls. In addition, the F2 hamsters derived from the DEN-treated P generation showed more frequent multiple organ involvement in tumorigenesis than the F2 controls. Several uncommon malignant tumours were detected in the F2 offspring, possibly the result of damage caused to germ cells by the prenatal exposure of F1 Syrian hamsters to DEN.