This standard includes a process for streamlined quality control (QC) of commercial microbial identification systems (MISs) that utilize multiple substrates and/or reagents to identify aerobic or anaerobic bacteria, yeasts, moulds, or yeastlike algae from culture. It specifies responsibilities of the manufacturer, distributor, and user. M50-A includes guidelines that may be followed when using an MIS of proven reliability to take a modified QC approach, rather than meeting requirements included in the Clinical Laboratory Improvement Amendments of 1988 regulations. The streamlined QC approach was developed following an evaluation of data provided by the American Society for Microbiology for a survey conducted to determine the QC failure rates of commercial MISs. The data showed a failure rate of less than 0.1% for all commercial MISs surveyed. This document is based on United States (US) regulations and will also serve as a useful resource for a wider audience. It is anticipated that M50-A will be used extensively in the United States and internationally to reduce resources spent on excessive QC testing.