WHO Laboratory Manual for the Examination and Processing of Human Semen. Semen analysis may be useful in both clinical and research settings, for investigating male fertility status as well as monitoring spermatogenesis during and following male fertility regulation and other interventions. This manual provides updated, standardized, evidence-based procedures and recommendations for laboratory managers, scientists and technicians to follow in examining human semen in a clinical or research setting. Detailed protocols for routine, optional and research tests are elaborated. The fifth edition includes new information on sperm preparation for clinical use or specialized assays and on cyropreservation, an expanded section on quality control in the semen analysis laboratory and evidence-based reference ranges and reference limits for various semen characteristics. The methods described are intended to improve the quality of semen analysis and the comparability of results from different laboratories.