Preparations with 4 percent Tetramisole or Levamisole hydrochloride were compatible in the mammary gland after application up to 40 ml/quarter (4 mg/kg body mass) for up to 6 milking times. 100 ml of the preparations were also clinically compatible in a single quarter (10 mg/kg body mass) on several days. After intramammary application of 30 ml/quarter (3 mg/kg body mass) Prototheca suppressing values in milk serum were evident for at least 6 hours. One application of 200 ml in one quarter has caused Prototheca suppressing values for 36 hours in milk serum up to dilution 1:4. Nilverm given to cattle in high dosage orally did not lead to Prototheca suppressing values in milk sera.