A new vacuum system has been designed and constructed for a Siemens Elmiskop I electron microscope in order to provide a cleaner environment about the specimen during normal use of the instrument, and to prepare the instrument for the addition of an ultrahigh vacuum specimen chamber forin situfilm growth studies. Liquid nitrogen sorption pumps are used on the upper and lower parts of the microscope column, and an Orb‐Ion pump is used to pump differentially on the large Siemens specimen chamber (with airlock). An impedance tube at the top and an impedance aperture at the bottom of the specimen chamber restrict the gas flow rate into the chamber to 7.04×10−3liter/sec. Under operating conditions the pressure in the upper and lower parts of the microscope is <2×10−5Torr, the (large Siemens) specimen chamber pressure is <2×10−6Torr, the hydrocarbon contamination rate is ∼0.7 Å/min, the specimen changing time is 2 min, and the plate changing time is 4 min. The corresponding figures in the original unmodified microscope are ∼2×10−4Torr, ∼2×10−4Torr,∼ 500 Å/min, 1 min, and 4 min. Further advantages are noiseless and vibrationless operation.