Summary A series of experiments on the ciliate Trithigmostoma steini was conducted in order to analyze interrelation of total protein contents between two daughter cells and their “adopted mother” (mother's sister) cell. We discuss the pattern of total proteins regulation in respect to the incremental model [1, 2, 4]. The results allow to reject the hypothesis of constant protein increment in Trithigmostoma steini. Instead we suggest that the increment tends to diminish when the true mother's content of protein is large. We also noticed a negative correlation between the length of the cell cycle and the initial protein content of the cell. However, one cell cycle is not a sufficient period to investigate this effect. The regulation processes observed in Trithigmostoma steini seem to be similar to those of other ciliates and we believe that they are based on molecular control mechanisms known for other eukaryotes.