An archaic term for a hypersensitivity reaction due to circulating antigen-antibody complexes (see ANTIGEN; ANTIBODIES), so-called because it was a recognised reaction to the administration of foreign SERUM which used to be given as a form of passive IMMUNITY before the days of antibiotics. A similar series of events can occur 1–3 weeks after the administration of drugs such as PENICILLIN and STREPTOMYCIN. It is characterised by fever, ARTHRALGIA and LYMPHADENOPATHY and is usually self-limiting as it resolves when the supply of antigen is used up.