A FIA method has been developed and fully characterized for the simultaneous detection of ammonia and glutamine in culture media. Ammonia detection is based upon a chem. method and does not require an electrode. This species diffuses across a hydrophobic porous membrane into an indicator soln., the absorbance of which is continuously monitored using a LED and a phototransistor. Glutamine was detd. by a difference method in which ammonia was measured before and after passage through a module contg. immobilized glutaminase. Very good linearity was obsd. in the range 0-4 mM for both species. Total anal. time was 22 min. This FIA method was used to accurately monitor ammonia and glutamine on line for over 600 h for a hybridoma culture performed in a hollow-fiber reactor. FIA measurements were in good agreement with off-line measurements. No instrument failures occurred, thanks to systematic cleaning and maintenance procedures. This FIA method is a very attractive tool for the monitoring, and possibly control, of continuous cultures over extended periods. [on SciFinder (R)]