This protocol was developed to label proteins in bacterial cells with antibodies conjugated to a fluorophore for fluorescence microscopy imaging. The procedure is optimized to minimize morphological changes and also to minimize the amount of antibodies needed for the staining. The protocol can also be used with primary antibodies conjugated to a fluorophore. The method has been verified extensively (van der Ploeg et al., 2013), but it should be noted that one case in Caulobacter crescentus (Hocking et al., 2012) has been reported in which the localization of a protein changed upon fixation by formaldehyde/glutaraldehyde. However, the localization of the same protein in E. coli did not change.