Brucellosis in humans is a zoonosis of greatly varied clinical image. It occurs on all inhabited continents. The course of the disease may be acute, sub-acute or chronic. The etiologic factors of brucellosis are small, aerobic Gram-negative rods of the genus Brucella, which currently contains ten species: B. abortus, B. suis, B. ovis, B. melitensis, B. canis, B. neotomae, B. pinnipedialis, B. ceti, B. microti and B. inopinata. In humans, the disease is caused mainly by: B. melitensis as the most pathogenic species, followed by B. suis, whereas B. abortus is considered as the mildest type of brucellosis. The natural reservoir of the germ and the source of infection in humans are infected domestic animals, primarily cattle, sheep, goats, as well as wild animals. Infection in humans occurs by penetration through damaged skin, conjunctiva, and more rarely via the alimentary route by the consumption of infected products. Especially exposed are: veterinarians, veterinary technicians, insemination service employees, zoo technicians, farmers working on multi-herd farms (production cooperatives), e.g. cattlemen, also private farmers, employees of slaughter houses and meat processing enterprises. A basis for diagnosing brucellosis are serologic tests which allow the detection of antibodies occurring in response to infection, performed with the use of the following methods: agglutination test, complement fixation test, Coombs test, 2-mercaptoethanol agglutination test, and Burnet's intradermal allergy test which detects the state of hypersensitivity of the infected organism to Brucella abortus rods.