AbstractA single SC injection of 2‐acetylaminofluorene (AAF) was given to pregnant C57BL/6 mice on day 15 of gestation, and the offspring subsequently given twice‐weekly injections of phorbol for 25 weeks. Control groups included: (1) untreated; (2) AAF‐treated mothers (kept under observation for 18 months, as with all the other groups); (3) untreated offspring of untreated mothers; (4) untreated offspring of AAF‐treated mothers, and (5) phorboltreated offspring of untreated mothers. The incidence of hepatomas in the phorbol‐treated offspring of AAF‐injected mothers was 8/74 (11%), as compared with 2/80 (2.5%) in the untreated offspring of AAF‐injected mothers. The AAF‐injected mothers themselves developed 3/36 (8%) hepatomas; while all the other control groups were free from liver tumours. The development of reticulum cell sarcomas, and of a few cases of lung adenomas, in the various groups, was presumably spontaneous. The results seem sufficiently encouraging, as a model for the study of systemic carcinogenesis, to warrant further attempts at two‐stage transplacental carcinogenesis, using other potential initiators and promoters.