Etiology of pleural effusion is diverse.Transudatory or exudative, benign or malignant, tuberculous or non-tuberculous pleural effusion can be distinguished by laboratory examination, so it is helpful to find the etiology of pleural effusion to diagnose the disease and guide therapies.Laboratory examinations of pleural fluid include routine, cytology, biochemistry, immunology and molecular biology examination.More and more researchers realize the importance of laboratory quality control before analysis in recent years.Since specimens belong to this part, it has attracted more and more attention in the laboratory.As tumor and tuberculosis are main causes of pleural effusion, most new projects and technologies are aiming at diagnosing malignant and tuberculous pleural effusion.These new projects and new technologies need to be appropriately evaluated (its advantages and disadvantages) before application to clinical and then are decided whether to carry out the project and technology.It can also help clinicians in the selection of projects.