Downshock treatment of the halotolerant Brevibacterium sp. JCM 6894 was a prerequisite for proline uptake which is a function for cell survival. Hydroxyectoine served as an effective stimulator for the proline uptake and cell survival of the downshocked cells of this strain. Duration of osmotic downshock, downshock strength, and the kinds of osmolyte affected the efficient rate of growth (ERG) and the uptake of proline. A shorter duration of osmotic downshock, that is <or=1 h, induced higher ERG values and stimulated proline uptake, compared with those of non-downshocked cells when incubated with hydroxyectoine and proline. These activities, however, were gradually suppressed with the prolongation of the duration of osmotic downshock. When the cells grown in KCl-containing medium were subjected to downshock treatment for 1 h, their activities were enhanced more remarkably than those of cells grown in NaCl-containing medium.