One thousand patients who received 1112 total joint replacements between 1966 and 1980 were followed up prospectively for an average of six years. These patients were not advised to take antibiotics prophylactically to cover subsequent dental or surgical procedures and, so far, only three cases of haematogenous infection at the site of the joint replacement have developed. Two hundred and twenty-four patients did subsequently undergo dental or surgical procedures and 284 patients developed infections in the respiratory tract, urinary tract or at multiple sites; none of these patients developed haematogenous infection. But of 40 patients who suffered recurrent skin ulceration and infection, three (7.5%) developed haematogenous infection of the replaced joint; two of these belonged to a group of 134 patients with rheumatoid arthritis. These results suggest that transient bacteraemia is not likely to infect a replaced joint in otherwise healthy patients. But an infected skin lesion producing chronic bacteraemia, or septicaemia due to a virulent organism, may well do so and patients with rheumatoid arthritis are at greater risk than those with osteoarthritis.