The growth rate of Escherichia coli ATCC 9637 was determined in a chemically defined (CD) medium with high osmolarity, 1-1.2 M. The addition of ectoine or glycine betaine to the medium resulted in a significant stimulation of growth rate for this strain. In the presence of ectoine derivatives, hydroxyectoine and homoectoine, cell growth was not stimulated to the same extent as when ectoine was added, but it was improved slightly. The acceleration of growth rate of E. coli ATCC 9637 at elevated osmolarity was ascribed to the accumulation in the cells of ectoine or glycine betaine added to the medium, both of which were proved to be genuine osmolytes in cells. Rapid uptake of ectoine by cells was confirmed when ectoine was available in the CD medium with high osmolarity. Since strain ATCC 9637 did not accumulate ectoine in the absence of an energy source, ectoine uptake might take place not only through cellular sensing of the external high osmolarity but through cellular functioning via energization.