Centrifugal elutriation was used to separate cells of Saccharomyces cerevisiae in balanced exponential growth according to position in the cell cycle. Macromolecular synthesis was examined. DNA synthesis was found to be periodic, but RNA and protein synthesis showed an exponential increase in rate. Two-dimensional electrophoresis was used to determine the rate of synthesis of individual proteins, with 111 of the more abundant cellular proteins selected for analysis from among the more than 1000 proteins that migrate in the system. All the examined proteins showed an exponentially increasing rate of synthesis.