In order to understand the role of the medium osmolality on the metabolism of glutamate-producing Corynebacterium glutamicum, the effects of saline osmotic upshocks from 0.4 osmol. kg(-1) to 2 osmol, kg(-1) have been investigated on the growth kinetics and the intracellular content of the bacteria. Addition of a high concentration of NaCl after a few hours of batch culture results in a temporary interruption of the cellular growth. Cell growth resumes after about Ih but at a specific rate that decreases with increasing medium osmolality. Investigation of the intracellular content showed, during the first 30 min following the shock, a rapid but transient influx of sodium ions. This was followed by a strong accumulation of proline, which rose from 5 to 110 mg/g dry weight at the end of the growth phase. A slight accumulation of intracellular glutamate from 60 to 75 mg/g dry weight was also observed. Accordingly, for Corynebacterium glutamicum an increased osmolality in the culture medium resulted in a higher specific rate of glutamate and proline synthesis during the growth phase.