Hospital transfusion services and blood donor centers have continued to rely on manual hemagglutination methods for pretransfusion compatibility testing. Automation with continuous flow and batch analyzers has been practical only for the largest donor centers. During the last 20 years, other methods of streamlining compatibility testing have evolved. Two of the most successful approaches have used microplates to perform liquid agglutination tests or solid-phase, red cell adherence tests. More recently, a gel test has been developed. On the basis of these technologies, increasing numbers of semiautomated systems for compatibility testing have become commercially available. However, these systems primarily address the needs of large donor centers. New technologies are needed to automate the transfusion services of hospitals and other small laboratories.