Partial hepatectomies were performed on five groups of rats which had been maintained on a diet containing 4-dimethylaminoazobenzene for various lengths of time. The effect of regeneration on the incidence of hepatic tumors was compared with that in similarly treated non-hepatectomized controls.

Regeneration, and the time of exposure to the carcinogen as well, were relatively effective in accelerating the rate of appearance of tumors, although not markedly so. These factors were without effect on final total tumor formation.

These findings support the concept that during chemical carcinogenesis tumor formation proceeds in stages.

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