Three hundred and twenty Chinese hamsters (Cricetulus griseus) (CH) were subcutaneously (s.c.) treated with 1/5, 1/10 or 1/20 the mean lethal dose (LD50) of N-dibutylnitrosamine (DBN) or N-nitrosomethylurea (NMU). In several respects these two substances produced the same organotropy in the CH as in the Syrian golden (SGH) and European hamsters (EH). DBN prolonged lung tumours and neoplasms of the injection site. NMU induced tumours of the injection site only.