Analysis of synovial fluid is of extreme importance for diagnosis and treatment of joint diseases. It is divided into general and special analysis. Analyses regarding colour, quantity, viscosity, transparency and formations of mucinous clots in synovial fluid are classified among general investigations. Less complicated microscopic investigations, such as those regarding number and differential picture of leucocytes, also belong to this group. In numerous cases, differential diagnostic problems may be clarified by previously mentioned analyses, which are quite rapid (especially in cases of suspected acute joint infection, arthritis caused by crystals, blood effusion into a joint and similar). Valuable data regarding the type of the joint disease can be obtained by special analyses (microbiological, immunoserological, biochemical) and examination of synovial fluid for crystals (polarising microscopy). Special analysis is an important guide in the planning of treatment.