A semi-on-line automated analysis for fermentation is presented. The system consists o f a modified commercial biosensor analyser YSI 27 and a Gilson dilutor injector. The results of direct glucose monitoring in fermentation broths are presented. Measurements, calibrations and washes are completely automated, with a m a x i m u m analysis frequency o f 16 per hour with dilutions. The detection limits are 50 mg/1 and 41 g/1 with g o o d linearity and a precision o f ___ 5%.