An electron microscope method for inspecting a liquid specimen and a reagent solution therefor. A culture medium and biological cells are put in the sample holder. A plugging agent is mixed into the liquid sample. The cells can be irradiated with a primary beam via a film. An image of the cells or information about the cells is obtained by detecting a resulting secondary signal. If the film is destroyed, the plugging agent plugs up the damaged portion of the film. Consequently, liquid leakage can be minimized.