Toluenised cells of Bacillus subtilis W23 synthesized the teichoic acid, poly(ribitol phosphate), from exogenous precursors. The synthesis was dependent on concomitant synthesis of the linkage unit that joins teichoic acid to peptidoglycan. Under conditions that reduced cell autolytic activity, a large proportion of the teichoic acid became linked to the cell wall, independently of peptidoglycan synthesis. The specific activity of the system was more than 30 times that of isolated membranes, so that activity could be measured readily in the cells from 2 ml of an exponential culture of bacteria.