After more than four decades of research into automation of the process of screening Papanicolaou (Pap) smears, attempts to develop commercially viable automated screening machines have increased in recent years. These developments have been made possible in part because of the improving price-to-performance ratios in computers and other electronics. Although the Pap smear has been responsible for a very significant decrease in mortality of cervical cancer over the past 40 years, concern has arisen over false-negative cases, with their effects on patients, and the associated legal liability, particularly in the United States. In addition, shortages of cytotechnologists, which have been exacerbated by new regulations limiting the number of slides that may be examined per day, have caused concern about handling the workload, which will probably increase as more individuals gain access to preventive health care. Automated screening machines can potentially allow detection of abnormal cases that are missed with conventional screening, although they may substantially increase the cost of Pap smears. The use of automated screening machines represents a change in the way cervical cytology specimens are processed, and with some machines, a significant change in the operation of the cytology laboratory. Current methods for processing and evaluating Pap smears have not changed significantly for the past four decades. This review discusses some of the principles of operation and practical aspects of automated screening machines.