We have developed a simple and accurate isocratic HPLC method, without any prederivatisation, for the determination of glucose, lactate, glutamine, glutamate, pyrrolidone carboxylic acid and alanine in samples from mammalian cell cultures. The method has been successfully validated with enzyme analysis for each of the compounds. Quantification of pyrrolidone carboxylic acid makes the correction for glutamine decrease due to chemical decomposition very simple and accurate, and avoids some possibly erroneous calculations. [on SciFinder (R)]