The growth and emetic toxin (cereulide) production of Bacillus cereus strains in defined culture media were studied. We found that a fully synthetic medium (CADM) allowed the production of emetic toxin and the addition of glucose enhanced it. By subtracting each amino acid from CADM, we found that only three amino acids, valine, leucine and threonine, were essential for growth and toxin production by B. cereus. The addition of high levels (50 mM) of leucine, isoleucine and glutamic acid decreased the toxin production. Other amino acids had no effect at this concentration.