This chapter describes body fluids, gastric analysis and sputum examination. Body fluids are lubricating fluids present within the body cavities. Body cavities include—pleural, peritoneal, pericardial and synovial. Normally, a small amount of fluid is present within the body cavities which keeps the surfaces moist and lubricated so that the movement of the adjacent or the opposing membrane surfaces occurs with minimal friction. Increase in the volume of the fluid in these cavities is known as effusion. Examination of synovial fluid is useful in the diagnosis of joint disorders such as infective arthritis (septic arthritis, rheumatic), gouty arthritis (metabolic disorder), rheumatoid arthritis (autoimmune disorder), and degenerative arthritis. Gastric analysis is performed in few diseases of the stomach. Gastric analysis includes the laboratory tests to measure gastric secretions and serum gastrin.