This paper aims at the estinetion of bianass concentration of fad-batchfernen tation processes bysimultaneoUsmeasuremsn t of substrate consumption, oxygen uptake and carbon dioxide production. & the basis of chsmical stoichionretry and elmental balance describing intracellular biochemical reactions, the instantaneous conservation balance equations for Sacchararlyce s osrevi.siaeandStreptanyces at&ofaciens arederived fortbepresen tpurpase. Egplication of these equations is disturbed by process randan errors. The process is also affectedby randcrn disturbance oannonly regarded as white noise. Extenc%d Kalxsan filter is used forestimatingstatevsriables. Twowhitenoisematrices sre obtainedaccordingtothe intensity of randcan errors snd that of disturbance. muter sinulation of the above nentionedtwo processes agreeswellwiththe experimantal datashcwingthe cellgrowthversustime. Adaptive estimation, extended Kalman fliter, cell concentration, elesentsl balances, S. cerevisiae S. &faciens. Intrcduction Cceputer-aid& operation of biochemical proces seshasdrawn -attention in recent years. State characteristics of bioreactors are expressed by state variables, operating parameters and culture parameters. Cell concentration,