Two lots of yoghurt were prepared to contain Listeria monocytogenes V7 (milk isolate, serotype 1) at an initial inoculum of 3 x 10 cells/g. and then were refrisgerated at 5 + 1 °C. Viable counts of L. monocyto genes as well as pH value of yoghurt were determined at O time and daily thereafter. L. monocytogenes survived until the end of the fourth day at a population of less than 10 cells/g. The pH value of yoghurt decreased sharply from 6.6 to 4.7 by the end of preparation, and a low value of 4.1 was reached at the end of the fourth day.