Bacteria on plant surfaces were examined using epifluorescence, bright‐field microscopy and an impression technique. Staining bacteria directly on the plant surface with phenolic aniline blue was found to be the best method to use for the determination of bacterial density. The effect on the estimation of population density of pretreatment of the plant with agents such as methanol and eosin yellowish was investigated. The average sizes of the bacterial populations on two freshwater plants,Rorippa and Lemna, estimated after staining by this method, were 5 times 106and 9 times 106bacteria cm‐zrespectiv