Staphylococcus spp. are the single most important cause of mastitis in dairy cows. Aiming for a rapid and sensitive method for detection of staphylococci, a magnetic bead-based enzyme-linked immunosorbent assay (ELISA) employing MAb for the detection of staphylococci in milk was developed. Pretreatment of the sample with lysostaphin increased the sensitivity of the assay. The method is specific for most of staphylococci which cause mastitis in bovines, detects between 10(4)-10(5) organisms per ml and takes three hours. Thus, the principle for staphylococci ELISA based on monodisperse magnetic beads is a way for rapid detection of staphylococci in milk and possibly also for detecting staphylococci by direct testing of other clinical specimens. The system may be automated.