Specific-locus test shows ethylnitrosourea to be the most potent mutagen in the mouse.

Abstract
Use of the specific-locus test to measure the frequency of transmitted gene mutations induced in mouse spermatogonia showed that ethylnitrosourea was by far the most potent mutagen yet discovered in the mouse. The dose used, 250 mg/kg, gave a mutation rate 5 times as high as had been obtained with 600 R, the most effective acute dose of X-rays. The most effective dose of ethylnitrosourea was 15 times more mutagenic than the most effective dose of procarbazine, which was previously the most effective mutagen for the mouse. Because of its high mutagenicity, ethylnitrosourea can serve as a model compound in exploring the effect of such factors as dose response, dose fractionation, sex and cell stage on the mutagenic action of a chemical. Ethylnitrosourea is clearly the mutagen of choice for the production of any kind of desired new gene mutations in the mouse.