Effective scattering cross sections for polystyrene in electron microscope specimens were measured through the microdensitometry of the images of polystyrene latex spheres recorded with an RCA Type EMU 3B electron microscope. Measurements were made at both 50 kv and 100 kv beam potential without an objective aperture, with a 40‐&mgr; aperture and with a 20‐&mgr; aperture. Cross sections per gram vary from 1.9 to 11×104cm2/g. The results are consistent with previous experimental data and are in reasonable agreement with theoretical calculations.