Our objectives in conducting this evaluation were to present an overview of a basic phacoemulsification system and its components, to describe the phacoemulsification procedure within the context of the operating principles of the system's components, and to compare two manufacturers' products. Specifications for additional phacoemulsification systems are available in the November 1989 edition of ECRI's Hospital Product Comparison System. Both of the evaluated systems enable a surgeon to perform a complete cataract extraction procedure by phacoemulsification. We rated both units Acceptable. In selecting a unit, users should consider performance, safety, human factors design, and manufacturer training and support. Although list prices vary widely among available systems, cost factors should not override clinical performance and safety requirements. While we measured certain engineering parameters, such as stroke length and ultrasound (US) output forces exerted on a medium, we stress that the results of these tests do not provide enough information to predict clinical performance. Clinical performance of phacoemulsification systems can be determined only by the experience of the clinicians who use them. Clinicians should review our evaluation thoroughly before making a purchasing decision. The information we present is useful for purchasing the evaluated or other available models because our criteria will guide users in assessing all components, and our findings and discussion on some aspects are common to many available systems (e.g., type of pump, irrigation and aspiration [I/A] characteristics). The in-depth clinical and technical information will help users to better understand principles, thereby helping them to better define their needs. Although we discovered a number of problems with the evaluated models, users should not assume that similar or other problems do not exist with systems that we did not evaluate. The willingness of manufacturers to cooperate in our studies and the knowledge they gain through participating may lead to the development of better products.