Whole cells of Bacillus sp., bacitracin-producing bacteria, were immobilized in polyacrylamide gel prepared by using 5% total acrylamide (95% acrylamide monomer and 5% N, N'-methylenebis acrylamide). Bacitracin production by the immobilized whole cells was examined by using various fermentation media. In starch-bouillon medium, the initial activity of immobilized whole cells for bacitracin production was 20 to 25% that of an equivalent amount of washed cells. With successive utilizations in 1% peptone as reaction medium, activity of the immobilized whole cells increased gradually and reached a steady-state maximum having a value of 80 to 90% of the activity obtained initially with washed cells, whereas the washed cells lost most activity when utilized successively. What appeared to be growth of the bacteria in the gel was observed by electron microscopy. Therefore, the activation of immobilized whole cells during successive utilizations apparently resulted from the growth of whole cells in the gel, especially at the gel surface.