The structure of bacterial suspensions of Escherichia coli M-17 has been investigated for cell counts of 10⁷, 10⁸ and 10⁹ ml^-1 in the 18-50 °C region by orientation conductometry, electron microscopy and ultraviolet absorption spectroscopy. From the experimental dependences of the anisotropy of the electrical conductivity of the suspension on the voltage of a sinusoidal electric field and the relaxation of anisotropy after switching off the field, the authors determined the size distribution functions of the bacteria at different concentrations and temperatures. It is shown that the size distribution functions of the bacteria determined by this method are in good agreement with those obtained in the electron microscope. From these functions in the suspension of E. coli M-17 they established three types of cells: electron-dense and electron-transparent bacteria and cell aggregates, the relative content of which varies with temperature and the cell count in the suspension (minimal number of aggregates and maximum content of electron-transparent cells were observed in the region of the temperature optimum of the habitat of the bacteria (32-42 °C)). It is concluded that this phenomenon may be explained by activation of the membrane transport systems of the cell in the 32-42 °C interval confirmed by ultraviolet absorption spectroscopy.