Haemophilus paraphrophilus is a normal inhabitant of the naso- and oropharynx and has been rarely reported as a cause of endocarditis. H. paraphrophilus is a slow-growing and fastidious gram-negative bacterium and belongs to the HACEK group. We experienced a case of infective endocarditis due to H. paraphrophilus. The organism was repeatedly isolated from the blood cultures of a 60 year-old patient presenting with high fever, chills, cardiac murmur, and change of mental state. The patient had a history of mitral and tricuspid valve replacements and had been followed up for complications of cirrhosis of liver such as esophageal varix and oral bleeding. The isolate was identified as H. paraphrophilus by the characteristics, including factor V requirement, negative indole, urea and ornithine decarboxylase and acid production from glucose and lactose. Antimicrobial susceptibility testing by the disk diffusion method showed that the organism was susceptible to ampicillin, chloramphenicol, tetracycline, trimethoprim/sulfamethoxazole, cefotaxime, ceftazidime, aztreonam, imipenem, and ciprofloxacin. The patient expired on hospital day 8, probably due to complications of cirrhosis of liver. To our knowledge, this is the first case of infective endocarditis caused by H. paraphrophilus in Korea. (Korean J Clin Microbiol 1999;2:95~100)