In a review of endocarditis caused by fastidious, slow-growing gram-negative rods, similarities in the spectrum of disease overshadow differences among cases grouped by specific organisms. Cardiobacterium hominis, Actinobacillus actinomycetemcomitans and Haemophilus species usually seed previously damaged cardiac valves presumably during bacteremia from an upper respiratory site. The clinical presentation resembles that of Streptococcus viridans endocarditis and is usually subacute or chronic. Despite bacteriologic cure, severe CHF and/or systemic embolization frequently develops during or following the course of antibiotics, resulting in significant morbidity and a high mortality rate. This report of nine cases diagnosed at five hospitals in a 7-year period suggests that endocarditis due to these organisms is more common than previously appreciated and frequently goes unrecognized. This is probably due to a lack of attention to the requirements for culture of this group of bacteria with propensity for granular growth in broth. We have proposed specific cultural techniques appropriate to the search for these organisms in patients with apparent culture-negative endocarditis.