Intra- and extracellular metabolite concentrations were determined for hybridoma cells grown in tissue culture flasks in batch culture. Significant differences were found for intracellular lactate and amino acid concentrations depending on the culture medium. AB2-143.2 cells cultivated in Dulbecco's modified Eagle's (DME) medium supplemented with 50 mM lactate exhibited intracellular lactate and glutamine levels of 40 mM and 4 mM, respectively, whereas cells grown in standard DME medium had low intracellular glutamine and 20 mM lactate concentrations. For cells cultivated in medium supplemented with 6 mM pyruvate, intracellular lactate levels were estimated at approx. 40 mM, but these cells also showed an increased intracellular alanine concentration of 22 mM. The higher alanine pools probably result from increased transamination of pyruvate under these conditions.