23 Valent pneumococcal vaccine is provided to the elderly through public health programs in many countries. However there is no clear recommendation regarding its route of administration (subcutaneous or intramuscular). In a randomised, observer blind study of 254 elderly subjects, the immunogenicity of a 23 valent pneumococcal vaccine was not influenced by its route of administration. A low rate of systemic adverse reactions was observed with the vaccine (subcutaneous and intramuscular both 6.3%). Local adverse reaction rates were; intramuscular 7.1% and subcutaneous 18.9% and these were predicted by: * Pre-vaccination antibody titres>1 microg/ml, odds ratio 22.4 (8.06-74.84) compared with pre-vaccination antibody titre<1 microg/ml. * Female gender, odds ratio 5.0 (1.85-14.83) compared with male gender. * Subcutaneous injection route, odds ratio 3.20 (1.13-9.13) compared with intramuscular injection route. * Female gender subcutaneous injection route, odds ratio 2.99 (1.10-8.70) compared with female gender intramuscular injection route. These data support the intramuscular injection of 23 valent pneumococcal vaccine, especially in elderly females.