Several different epidemiological typing methods have been used in studies of coagulase-negative staphylococci; these include biotyping, antibiotic susceptibility pattern analysis, serological typing, phage typing, slime production detection, protein profile analysis, immunoblot fingerprinting and DNA typing. The most frequently used tests are antibiotic susceptibility and extrachromosomal DNA banding patterns. Comparison of chromosomal DNA restriction patterns is facilitated when the fragments are separated by pulsed-field electrophoresis. Typing variations occur quite frequently even in isolates of demonstrated clinical significance. Caution should therefore be exercised in denying the clinical relevance of coagulase-negative staphylococci, even when successive isolates show distinct typing differences.