Using two-dimensional electrophoresis, the patterns of polypeptide expression of a wild type and an hns mutant of Escherichia coli were examined in exponential and late stationary phases. The same procedure was used for a kinetic study of proteins synthesized during the first 60 min following inoculation into fresh complete medium. The present study focusses on 35 polypeptides differentially synthesized according to the strain and/or the growth phase. One of the most striking and unexpected observations in this work was a strong and transient synthesis of H-NS in the wild-type strain just after the nutritional upshift.