A new Flow Injection Analysis (FIA) system was developed that permits the on-line monitoring of glucose. This information may be used to identify the biomass concentration. The proposed manifold allows the automatic analysis of glucose from 0 to 90 g/L. The results are in agreement with the analyses provided by HPLC. The system was applied to on-line monitoring of substrate in several Candida rugosa batches grow without detecting mechanical or biochemical problems. This information was linked to a Extended Kaiman Filter (EKF) recursive estimation scheme to identify the vector state of the system. Index Entries: Flow Injection Analysis; on-line glucose analysis; biomass identification; Candida rugosa. © 1990 Humana Press Inc.