A retrospective study of 125 patients presenting to the City Hospital, Edinburgh, with proven pneumococcal pneumonia showed that pneumococcus serotype 3 remains the most prevalent and that since 1970 the distribution of serotypes has remained virtually constant. The frequency of diagnosing pneumococcal pneumonia is increased by the use of countercurrent immuno-electrophoresis (CIE) of sputum. In this series, 25 per cent of patients with negative sputum culture but radiological evidence of pneumonia, were diagnosed by means of this method, which was overall more helpful in making the diagnosis than blood cultures. All nine deaths in this series were in those over 65 years of age.