The cases were studied of 109 patients admitted to the 2nd General Medical Division of the Umberto I Hospital in Turin in the course of a year. The study revealed 99 bacterial infections and 10 atypical forms including 7 mycoplasma pneumoniae and 3 virus infections. The importance of suspecting atypical pneumopathies is therefore emphasised and despite the technical difficulties that may at times arise, tests for the less common aetiological agents are recommended.