An epidemiological study on 35 strains of Staphylococcus epidermidis was conducted in Juntendo University Hospital between 1994 and 1996. The strains were isolated from blood and blood vessel catheters. Three epidemiological markers; PFGE type (pulsed-field gel electrophoresis using SmaI), biotype by STAPHYOGRAM and antibiotype (antibiotic resistant pattern) were used. There were 12 types in PFGE type, 6 types in biotype and 7 types in antibiotype. 1. The predominant types were PFGE type A (57.1%), biotype 1 (62.9%), and antibiotype I (resistant for oxacillin, ampicillin and gentamicin; 34.3%) in Juntendo University Hospital. 2. The strains with antibiotic V-VII (resistant for over 6 antibiotics) showed only PFGE type A and B. All strains with PFGE type B showed biotype 4-6 (negative nitrate reduction strain). 3. The strains having PFGE type A and B were isolated from various patient wards. The strains showing PFGE type A and antibiotype I were isolated from the pediatric ward. 4. There was no strain with PFGE type C or D in 1996. 5. Three patients in whom S. epidermidis was frequently isolated for a few months had the same types of PFGE type, biotype as well as antibiotype.