SUMMARYThe synthesis of low mol. wt. RNA has been studied in KB cells infected with adenovirus type z after labelling with 3H-uridine or ~2p. An increasing amount of virus-coded VA RNA is detected from 8 h after infection onward. The rate of synthesis of tRNA is unchanged up to 16 h after infection and thereafter decreases; from 24 to 48 h after infection, the specific activity of tRNA is about 6o ~o of the control value. The specific activity of cellular 5S RNA increases from 12 h after infection. When the tRNA is analysed by a two-dimensional gel electrophoresis system resolving the tRNA into 42 to 47 spots, changes in synthesis of tRNA in individual spots are seen. From 8 to IZ h after infection, an increase in the relative rate of incorporation into RNA is observed in 7 spots, while a significant decrease is detected in 8 spots. From I2 to I6 h after infection, incorporation into RNA is increased in 6 spots, but is most marked (sevenfold) in I spot. A decrease of incorporation into RNA in 6 spots is observed at the same time. From 24 to 34 h after infection, an increase in synthesis of RNA in 8 spots is observed and a decrease also in 8 spots. Incorporation into RNA in 2 spots is virtually shut off.