The specific monoclonal antibody productivity (qMab) of a murine hybridoma (CC9C10) increased with incubation temperature in the range 33°C to 39°C. qMab was constant at each temperature and was independent of the phase of culture. The qMab increased 97% at 39°C and decreased by 21% at 33°C compared with controls at 37°C. Specific rates of substrate (glucose and glutamine) utilization and byproduct (lactate and ammonia) formation also increased with temperature but the yield coefficient, YLac/Llc' was constant for 33°C to 39°C and YAmm/Gin was constant for 37°C to 39°C. YAmm/Gin at 33°C was lower than the control. Changes in specific nucleotide concentrations and ratios were monitored by analysis of intracellular nucleotide pools. The NTP ratio, (ATP + GTP)/(UTP + CTP), increased and the U-ratio (UTP/UDP–GNac) decreased during the course of each culture, whereas the adenylate energy charge, (ATP + 0.5ADP)/(ATP + ADP + AMP), remained relatively constant at a value 0.8. The relative content of UDP-/N acetyl galactosamine, UDP-N acetyl glucosamine, and NAD increased with incubation temperature, whereas the relative ATP content, SA(ATP + ADP + AMP)/SU (UTP + UDP-sugars) ratio, purine/pyrimidine, ATP/GTP, and U-ratio decreased at higher incubation temperatures. It is possible that these nucleotide parameters may have a regulatory role in the changes of qMab observed at the higher temperatures. © 1994 John Wiley & Sons, Inc.