Aims: To examine the rate and the extent of spore formation in Anoxybacillus flavithermus biofilms and to test the effect of one key variable -temperature - on spore formation. Methods and Results: A continuous flow laboratory reactor was used to grow biofilms of the typical dairy thermophile A. flavithermus (strain CM) in skim milk. The reactor was inoculated with either a washed culture or a spore suspension of A. flavithermus CM, and was run over an 8 center dot 5 h period at three different temperatures of 48, 55 and 60 degrees C. Change in impedance was used to determine the cell numbers in the milk and on the surface of the stainless steel reactor tubes. The biofilm developed at all three temperatures within 6-8 h. Spores formed at 55 and 60 degrees C and amounted to approx. 10-50% of the biofilm. No spores formed at 48 degrees C. Conclusions: The results suggest that both biofilm formation and spore formation of A. flavithermus can occur very rapidly and simultaneously. In addition, temperature variation has a considerable effect on the formation of spores. Significance and Impact of the Study: This information will provide direction for developing improved ways in which to manipulate conditions in milk powder manufacturing plants to control biofilms and spores of A. flavithermus.