The natural contamination of commercially available potato powder was used as background flora with an aerobic plate count at 308C of 4310 cfp /g (according to ISO 4833;Anonymous, 1991) and Bacillus spp. count of 63 10 cfp /g. Part of the Bacillus spp. was confirmed as B. cereus. As the level of B. cereus was near the detection limit of 10 cfp /g, it was decided to approve this batch of potato powder for use in this study, with a comment that in the trials results from the blank potato samples can be found positive for B.cereus at a very low level. B. cereus NCTC 11143,the reference strain for emetic toxin production, was cultivated in BHI for 20 h at 308C. The BHI was then diluted 1:100 in peptone salt solution and streaked onto 10 PEMBA plates ([ 16 cm, 1 ml perplate).