In this study we have established a method for screening a collection of strains, from the Bacillus cereus group of bacteria, for biofilm formation, including soil isolates, strains from culture collections, reference strains, dairy isolates, and clinical strains from different types of human infections. Certain strains from the B. cereus group, which includes the opportunistic human pathogen B. cereus, insecticidal B. thuringiensis, and the obligate human and animal pathogen B. anthracis, are known to have the ability to form biofilm, an attached state in which cells are closely packed and firmly attached to each other and usually a solid surface. In biofilm, microorganisms aggregate and excrete a protective and adhesive matrix of a polymeric, usually carbohydrate-containing, substance. The matrix may provide beneficial functions, such as protection from antibiotics and the immune system during infection and giving bacterial cells the ability to communicate during growth. Biofilm formation is known, at least for certain bacterial pathogens, to contribute to the aetiology of human disease, exemplified by Pseudomonas aeruginosa infections in cystic fibrosis patients.In this study 81 strains have been screened for biofilm formation, resulting in the confirmation of 7 strains, which form biofilm. The ability to form biofilm has not been observed to specifically correlate with strain origin; however strains isolated outside their natural environment (soil and insect intestine) have shown a higher propensity to form biofilm. We have also initiated gene disruption studies in a candidate regulatory gene, the pleiotropic transcriptional regulator plcR, to reveal its possible involvement in biofilm formation in Bacillus cereus ATCC 10987, a strain closely related to B. anthracis, isolated from spoiled cheese in the 1930s.