Summary When one wishes to measure with accuracy the œstrogenic activity on vaginal smears, it is necessary to study at the same time the « acidophilic index » the « acidophilic index. » the « pycnotic index » and also the value A/P i.e. acidophilic index/pycnotic index Oestrogenic activity is characterized by the increase of those two values but it seems that they need a different treshold of œstrogenic activity to be modified. This method makes possible to gain some information on the quality of the œstrogenic reaction and also on the duration of the activity of œstrogenic drugs. Besides, when the value A/P is higher than 1, acidophilia is abnormal and it becomes impossible to appreciate exactly the degree of the œstrogenic reaction. Monochromatic technics do not permit a comparativo study of these values. They must be discarded. It must be emphasized that polychromatic methods, like that described by Shorr, are not more difficult than monochromatic technics.