Morphological effect of phenol on Spirilla cells was observed with a light microscope, a darkfield light microscope, a scanning electron microscope and a transmission electron microscope. Spirilla strains used were Spirillum itersonii and Spirillum peregrinum. As a control, Escherichia coli was used. The experimental results obtained are as follows : 1) Cells of Spirilla and E. coli showed a remarkable elongation at the subinhibitory concentrations (SIC : Sp. itersonii