Effects of millimeter waves (MMW) at the frequency of 51.755 GHz were studied in logarithmic and stationary E. coli cells at various cell densities. The changes in the genome conformational state (GCS) were analyzed by the method of anomalous viscosity time dependence (AVTD). Before lysis, the cells were adjusted to the cell density of 4x10(7) cells/ml and all AVTD measurements were run at this cell density. Stationary cells responded to MMW by increase in AVTD, while the same MMW exposure decreased AVTD in logarithmic cells. MMW effects depended on cell density during exposure and were stronger for stationary cells. The observed dependence on cell density suggested a cell-to-cell communication between cells during exposure to microwaves. Decrease in power density (PD) resulted in more striking differences between responses at different cell densities. The data provided evidence that intercellular communication in response to MMW depended on cell status and PD of microwaves. The MMW effects were studied in more detail at low intensity of 10(-17) W/cm(2) in the range of cell densities 4x10(7) to 8x10(8) cells/ml. The obtained sigmoid-like dependence of MMW effect on cell density saturated at approximately 5x10(8) cells/ml. The dependence of MMW effect on cell density was very similar in this study and in previous studies with weak extremely low frequency (ELF) electromagnetic fields (EMF). The data suggested that cell-to-cell communication might be involved in response of cells to weak EMF of various frequency ranges.