[Natural occurrence of progesterone in commercial milk products (author's transl)].

By means of radioimmunoassay the concentrations of progesterone in commercial milk products were determined. The values range from 1.4 ng/ml (skin milk) to 300 ng/g (butter). The results show a close correlation between progesterone and fat contents in milk products. It is discussed that - due to recent progress in analytical methods - hormones in their natural occurrence in food are now measurable in micro-quantities which were not yet considered to be of biological importance; these findings should provoke a revision of terms like "free of hormones" in the sense of "zero tolerances".