The respiratory activity of Escherichia coli K-12 was inhibited by high NaCl concentrations. The addition of compatible solutes such as proline and ectoine led to the recovery of the respiration of E. coli K-12 inhibited by 1 M NaCl to a similar extent as did the addition of glycine betaine. Glucose, an exogenous substrate for the stimulation of respiratory activity, was not taken up by the cells in the presence of 1 M NaCl, but active uptake of glucose was observed following the addition of compatible solutes. As a result, we obtained a good correlation between respiratory activities and glucose uptake rates, suggesting that the glucose uptake activity inhibited by high NaCl concentrations was facilitated by these solutes. The addition of proline did not lead to cell proliferation in the minimal medium containing I M NaCl, although the cells took up proline quite efficiently under high osmolarity. On the other hand, cell growth occurred after a lag time in the medium containing glycine betaine or ectoine in place of proline. Similar actions of the compatible solutes mentioned above were observed for E. coli ATCC 9637.