The bacteriological characteristics and susceptibility to antimicrobial agents of 108 clinical isolates of Staphylococcus lugdunensis and Staphylococcus schleiferi are described. Fifty out of 108 isolates were considered to be responsible for 16 documented infections, including some severe infections (endocarditis, bacteraemia, osteitis). A number of bacteriological characteristics enabled the identification of these species in the clinical microbiology laboratory: the absence of coagulase and protein A, and the presence of a fibrinogen affinity factor and thermonuclease along with other biochemical characteristics (ornithine and arginine decarboxylases, carbohydrate acidification, novobiocin susceptibility) differentiated these new species from other staphylococci; however, they did not possess virulence markers such as toxins or haemagglutinin, but were haemolytic. In this series, almost all isolates were susceptible to 22 antibiotics and 4 antiseptics representative of the main groups of antimicrobial agents. More information is needed on the ecology and epidemiology of these new opportunistic pathogens.