The authors have shown using literature data the complexity of diagnostics of the syndrome of a pleural exudate which can be a main manifestation in most cases of pleural cavity diseases. Late diagnostics of an exudate creates great difficulties during a process verification. Two groups of patients have been observed using different systems of diagnostics of an exudate. Basic group consisted of 117 patients and the first method of radiodiagnostics was ultrasonoscopy. A Traditional roentgenography was used for patients from comparison group. Complications in the form of considerable pleural stratifications and diaphragm deformation have been noted in comparison group 4.7 times oftener than in the control group.