A new technique is given of the absolute calculation of parasitic Protozoa in fishes. The mucus from the body and gills of fishes was mixed with such volume of water (V) that the drop of mixture (v) was clearly seen under themicroscope. The calculation of Protozoa was done in a sample from three drops of mixture covered with three slides (S). From 50 to 100 viewing fields were seen the them and an average number of Protozoa in one field was calculated. The total number of Protozoa in one fish (N) was equal to an average number of parasites in a viewing field (n) multiplied by the total number of viewing fields (m) which could be obtained at the examination of the whole mixture. The latter was calculated conventionally (see articles).