CDP-glycerol pyrophosphorylase, CDP-ribitol pyrophosphorylase and poly(ribitol phosphate) synthetase activities have been measured in cultures of Bacillus subtilis W23 as they became phosphate-starved either in batch culture or during changeover from potassium limitation to phosphate limitation in a chemostat. The results indicated that repression of synthesis of all three enzymes occurred at the onset of phosphate starvation and that this was accompanied by inhibition of inactivation of CDP-glycerol pyrophosphorylase and poly(ribitol phosphate) synthetase. These results show that the initial response to phosphate starvation involves more than inhibition of one enzyme as proposed by Glaser and Loewy [Glaser L. and Loewy, A. (1979) J. Biol. Chem. 254, 2184-2186]. Synthesis of both linkage unit and poly(ribitol phosphate) are inhibited independently.