The experiment was carried out on 36 one-day-old chickens fed to appetite a starter feed for broilers up to the age of 11 days. At this time 6 chickens (group zero) were sacrified. The remaining birds were divided into 3 groups: control (C), undernourished (U) and realimented (R). Two isocaloric diets with different protein content (12.9%-LP and 22.6%-HP) were force fed. The experiment was divided into two periods: during the first the mean body weight increased from 134 to 250 g and during the second-from 250 to 450 g. Throughout the experiment chickens C were fed the HP diet, chickens from U group the LP diet. The R group received LP diet and then, in the second period, HP diet. At the end of the first period 6 chickens from the C group and 6 from the U group, and at the end of the second period 6 chicken from C, U and R groups were sacrified to determine RNA polymerases activity in liver and breast muscle. Applied feeding regime had no significant effect on polymerase I and I I activity in the liver. On the other hand it evoked significant increase of activity of these enzymes in breast muscle of R chickens. This suggests possibility of regulation of protein biosynthesis on the level of transcription by changing either content or activity of RNA polymerases.