Intramammary infection of the dairy cow is much less common than 40 years ago due to the impact of a control programme. This has changed the aetiology of the infection. The problem remains one of the costliest affecting farm animal health, estimated at pound 300 million annually in the UK. The successful control relies much on antibiotic treatments. The use of antibiotics in food animals is under challenge, particularly use of broad spectrum, multicomponent products and use of prophylactic treatment. Recent research has confirmed that antibiotic treatment is practical and cost-effective. Moreover, it remains essential for animal welfare.