Biofilm-formation in Staphylococcus epidermidis depends on the expression of the icaADBC operon encoding the enzymes required for the synthesis of polysaccharide intercellular adhesin (PIA). Different S. epidermidis strains vary widely in the degree of PIA and biofilm that they produce. In 11 clinical S. epidermidis strains we analyzed the biofilm-forming capacity in relation to the amount of ica expressed in static biofilm cultures. In mid-exponential growth phase no correlation could be detected between the level of ica transcription and the biofilm-forming phenotype. When the different strains were grown under conditions leading to a biofilm-negative phenotype, ica-expression was highly upregulated. Sequence analysis demonstrated that the observed differences were not due to major mutations in the ica promoter region but apparently to other strain-specific regulators.