Starting point for this study was the urgent need for replacement of the contemporary mode of acute toxicity testing of chemicals in vertebrates (LD50-test) by an experimental model with equal power that can be performed on non-pain sensitive matter. For this purpose, a testing procedure ought to be developed using a non-pathogenic microorganism as testing object that is available at any time, easy to cultivate, and in its indicative power equivalent to the LD50 test in mice, rats, and other laboratory animals. Such an organism has been found with ordinary yeast (baker's yeast, brewer's yeast, Saccharomyces cerevisiae) which can always be obtained in good quality. This procedure (shortly denominated as 'yeast test' offers several advantages: It is rather simple, inexpensive, outstandingly well reproducible, and it can be carried out conveniently also in routine experiments. The results correlate well with those furnished by the customary methods of acute toxicity testing.