Between 1977 and 1988 in the Enschede hospital 72 patients were seen with bacterial arthritis of one or more joints. Staphylococcus aureus was most frequently the causative agent (52%) and the knee was the most frequently infected joint (42%); the mortality rate was 11%. Complete restoration of pre-existent function was seen in 52% of the affected joints. In patients with severe deterioration of joint function after the bacterial infection, the period between the first symptoms and start of treatment (mean 30 days) was significantly longer than in patients with no or moderately deteriorated joint function (mean 10 days). The primary focus was mostly a skin infection, predominantly localized on the lower extremities. Half of all cases of bacterial arthritis occurred in patients with rheumatoid arthritis (RA). We therefore conclude that patients with RA and skin infections, especially if localized on legs or feet, should be treated without delay and that one should not hesitate to prescribe antibiotics. Erythrocyte sedimentation rate (ESR) was less than 20 mm after one hour in 13% and blood leucocyte count less than 10 x 10(9)/liter in 55% of all patients, showing that a normal ESR and/or blood leucocyte count do not exclude bacterial arthritis. In 4 out of 9 patients with infected prosthetic joints the infection resulted in loosening of the joint, before antibiotic treatment was started. In the other 5 patients bacterial arthritis recurred, in one patient resulting in loosening of the joint, only shortly after stopping long-term successful antibiotic treatment (6-24 months). Thus, we feel that lifelong treatment with antibiotics is a reasonable alternative in cases, where the risk of surgery is very high.