A system for the independent control of ammonia and glutamine in a hollow-fiber reactor has been developed. Online anal. of the two chem. species was performed using FIA. A custom-made program has been written to fully automate the FIA, to perform measurements, calibrations and data acquisition, and to activate two peristaltic feed pumps. Diagnostic tests were also automatically performed in order to identify, and in some cases eliminate, erroneous measurements and calibrations due to instrument failures. For this purpose, a visual programming language (LabVIEW) has been chosen. Ammonia concn. was controlled by varying the medium supply rate to the hollow-fiber reactor, which was shown to behave like an ideal-stirred tank reactor. The glutamine concn. was controlled through the intermittent activation of a pump delivering a concd. soln. of this species to the reactor. This control system was tested with a culture of hybridoma cells at three different ammonia and one glutamine set-points. The hollow-fiber reactor was successfully operated automatically for more than 1200 h with ammonia and glutamine concns. accurately controlled at non-limiting levels. The visual programming environment was found to be reliable and highly suitable for the development of custom programs for bioprocess control. [on SciFinder (R)]