A comparison of catabolic capacity was made between S. cerevisiae cells subjected to 24 h carbon or nitrogen starvation. The cells were shifted to starvation conditions at the onset of respiratory growth on ethanol in aerobic batch cultures, using glucose as the carbon and energy source. The results showed that the catabolic capacity was preserved to a much larger extent during carbon compared to nitrogen starvation. Nitrogen starvation experiments were made in the presence of ethanol (not glucose) to exclude the effect of glucose transport inactivation (Busturia and Lagunas, 1986). Hence, the difference in catabolic capacity could not be attributed to differences in glucose transport capacity during these conditions. In order to understand the reason for this difference in starvation response, measurement of protein composition, adenine nucleotides, inorganic phosphate, poly phosphate and storage carbohydrates were performed. No clear correlation between any of these variables and catabolic capacity after starvation could be obtained. However, there was a positive correlation between total catabolic activity and intracellular ATP concentration when glucose was added to starved cells. The possible mechanism for this correlation, as well as what determines the ATP level, is discussed.