An experimental procedure was investigated to simultaneously determine the amounts of adsorbed cationic surface-active agents on baker's yeast as well as growth-inhibition of the yeast, and the following one was proved to be satisfactory : A centrifugetube containing a suspension of 10 mg (in wet weight) baker's yeast in 4 ml phosphate-buffer of pH 7 with an addition of one ml of a surface-active agent, solution each in different concentration, is incubated for 10 minutes at room temperature

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... then centrifuged. The precipitated yeast-cells are twice washed with each 5 ml of sterilized water and finally are made up to 10 ml with water. One drop of the yeast-suspension is inoculated into 10 ml of a Reader broth and the growth is measured turbidometrically by absorbancy at 610 mp after the incubation for 18 or 42 hours. The surface-active agent in the supernatant and washed water which has been separated from the yeast-cells, is determined colori metrically by the eosine-chloroform-extraction method.