Synchronized oscillating cultures of Saccharomyces cerevisiae CBS 426 exhibit periodic oxidoreductive metab. The changing metab. is detectable by in situ heat-flux calorimetry in the BSC 81, which was operated as a chemostat in these expts. The measured metabolic heat flux oscillated in phase and with the same period as the other monitored process variables (CER, The authors', and DO) at the diln. rates studied (0.12 and 0.14 h-1). There was a difference of 2 W L-1 between the min. and max. of the oscillating heat flux. During these synchrony oscillations, the proportionality const. between heat dissipation and oxygen consumption was not const., but reached a max. value during each cycle. Data gathered from a sep. expt. with the same strain in a std. lab. bioreactor (D = 0.071 h-1) clearly corroborated the biol. nature of the oscillations. The oscillatory character of metab. is none other than a reflection of the cell cycle, which is punctuated by specific landmark events. Based on these results, a correlation between the heat dissipation and the specific cell cycle classes is proposed. [on SciFinder (R)]