This new blood test for infection is based on the phenomenon of leukergy in which white cells agglomerate in the peripheral blood of patients with inflammatory diseases. It was used in 26 patients with proven bone or joint infection and was positive in 25. The leukergy test was more accurate than the ESR, white cell count or blood culture. The percentage of cells agglomerated correlated with the clinical severity of the infection and the test detected reactivation of the septic process better than the other haematological tests. It is a rapid and inexpensive method which is useful in the diagnosis and management of bone and joint infections.