PURPOSE: Results of bacterial cultures and susceptibility tests in the neonatal period have shown changes according to the year they were reported, and the increase in pathogenic organisms has become a topic of great interest. This study was carried out to determine the trend in the occurrence of microorganisms and susceptibility testing results conducted on neonates from the newborns hospitalized in the NICU at Hanyang University Hospital during the past 1- years. METHODS: The laboratory data of microorganisms isolated by culture of various specimens from the NICU from January, 1986 to December, 1995 were retrospectively analyzed. The study period was divided in two 5-year periods. RESULTS: 1) The total number of neonates in the first half was 6,392, and 8,364 in the second half. Of these, positive blood cultures were observed in 62(1.0%) and 166(2.0%), respectively. Isolation from other specimens totalled 834(450 in the first half and 384 in the second). 2) There was a total of 13 specimens other than blood, from which bacteria were isolated. There 380 urine specimens and 20 umbilical secretions in the first half and 167 bronchial secretion and 101 umbilical secretions in the second. 3) The microorganisms cultured in the first half included 215 Gram positive, 232 Gram negative organisms, and 3 fungi. Common organisms included 119 cases of E. coli(26.4%), 66 cases of MSSA(14.7%) and 64 cases of CNS(14.2%). In the second half, there were 182(47.4%) Gram positive, 192(50.0%) Gram negative organisms, and 10(2.6%) fungi. The most common organisms were MRSA(123 cases, 32%), E. cloacase(56 cases, 14.6%), CNS(29 cases, 7.6%), and Klebsiella (29 cases, 7.6%). 4) There were a decrease in organisms susceptible to Oxacillin, Gentamicin, Cephalothin, and Ampicillin in the second half. CONCLUSIONS: The changes in the NICU during the past 10 years include a great increase in MRSA, Enterobacter, and Candida, reflecting the increasing trend of nosocomial infections. Furthermore, there was an increase in resistance to Oxacillin and Gentamicin while there was good susceptibility to Vancomycin and Chloramphenicol even in the second half.