The broad antibacterial spectrum of co-trimoxazole makes it a suitable agent for the treatment of a wide variety of infections involving most systems of the body. After 10 years of use in clinical practice in the United Kingdom resistance to the combination oftrimethoprim and sulphamethoxazole remains relatively low. Preparations of co-trimoxazole for parenteral as well as oral administration have recently become available thus increasing the usefulness of this agent in the therapy of serious infections. The good tissue penetration of trimethoprim is a further important factor in these conditions. Haematological adverse reactions and rashes can complicate therapy with cotrimoxazole and the drug should, therefore, be used with caution in sick patients. Most ofthe side-effects are probably related to the sulphonamide component. Cotrimoxazole should not be used in pregnancy. In our experience co-trimoxazole has proved to be effective in the therapy of septicaemia, including typhoid fever, and also in the management of severe bacillary dysentery, typhoid carriers and acute brucellosis. Other indications include infections in neutropenic patients, Pneumocystic carinii infections, neonatal meningitis, respiratory tract infections and pyelonephritis especially when associated with prostatitis.