An ultrahigh vacuum field-ion microscope has been modified to incorporate both a continuous flow cryostat and a specimen airlock. The design is simple in construction and operation, robust, and needs only the minimum of facilities for its manufacture. Following the specimen change it is possible to image a specimen at a background pressure of better than 1 n Torr within 30 min. The economical operating temperature range is down to 12K with a stability better than +or-0.1K h-1. The design can be adapted, without difficulty, for a wide variety of ultrahigh vacuum applications.