On the question of the carcinogenic action of hydrazine--evaluation on the basis of new experimental results.

Hydrazine has not previously been shown to have any carcinogenic action in man. After the administration of probably clearly toxic doses (the data in earlier publications are very fragmentary) or doses severely irritating to the sensitive nasal epithelium of the rodent over a large part of its life, hydrazine was shown in the majority of the studies described in the literature to be carcinogenic in rodents. Even under these severe experimental conditions, however, the carcinogenic action was not very pronounced or was even very weak. In the study in mice described below, which was carried out according to modern guidelines, no carcinogenic action was detected for hydrazine even after the administration of toxic doses over the entire lifespan of the animals. Administration of a still higher dose would have conflicted with all current recommendations. On the basis of the results available in the literature, indirect alkylation of DNA was assumed to be the mechanism of the carcinogenic action of hydrazine. According to the current level of knowledge, this effect, like the mutagenic and the carcinogenic action of the substance, is closely linked with the toxic activity of hydrazine. Overall, hydrazine should be regarded as a substance having a probably indirect weakly carcinogenic action after toxic doses administered over the entire lifespan.