Glutaminase and glutamate oxidase were immobillzed into a gelatin support fixed on a pO2sensor. The overall activity (02consumption) was correlated to glutamine concentrations range from 0.2 to 2mM. The sample oxygen content dependence of the signal was minimized by the support properties. Measuring time for each sample was 2 minutes including response data treatment and rinsing steps. On repeated use, the electrode signal for 0.5mM was stable for 300 assays at least. This technique has been applied in different mammalian cell cultures.