Summary A set of 18 bacteriophages was used to type 240 coagulase-negative staphylococci; 75·5 per cent. of the strains were lysed by one or more of the phages, 53 per cent. at RTD and a further 22·5 per cent. only at RTD X 1000. Most of the reactions at RTD could be grouped into seven main patterns. The relative frequency of occurrence in cultures from patients with lesions was somewhat different from that in cultures from nose swabs from healthy persons. In spite of careful control of technique, variation in phage-typing patterns was observed. The amount of variation appeared to be rather similar to that encountered in phage typing of Staph. aureus. Serial studies of the nasal flora indicate that some persons carry the same strain for a long time, but that others carry a strain only transitorily. Simultaneous carriage of two distinct strains occurs frequently.