The current and emerging technologies for detecting and characterizing human leukocyte antigen (HLA) alloantibodies provide powerful tools for predicting the risk of immunological response to a transplant. Clinical and Laboratory Standards Institute document I/LA29-A--Detection of HLA-Specific Alloantibody by Flow Cytometry and Solid Phase Assays; Approved Guideline describes criteria for optimizing methods that utilize flow cytometry and other conventional and multiplex platforms. The intended audience includes solid organ and stem cell transplant laboratories, manufacturers of systems for histocompatibility testing, and organizations that manage organ sharing.