On the basis of an epidemiological study on recently onset, possible reactive arthritides in Oslo we propose a programme for diagnostic evaluation. Disease symptoms and signs provided little help for an ethiological diagnosis. Therefore a variety of diagnostic tests and examinations are recommended in order to obtain a correct diagnosis; such as clinical examination, chemical and serological blood tests, bacteriological examinations from throat, of stools and of specimens from urethra-cervix, examination of synovial fluid and synovial tissue and X-ray examination of affected joints, sacroiliacal joints and lungs. About one third of the recently onset arthritides in the Oslo study were diagnosed as reactive arthritis, one third as possible reactive arthritis and another third as inflammatory arthritides.