Previously, it was reported that the growth of lactic acid bacteria growing in milk was accelerated by an addition of chlorella into it. Although the chlorella is an important food protein source, the utilization of the other components in it may have also a significance. The authors studied on the natures of the growth stimulating factors in chlorella. The factors readily extractableby diluted acids stimulated the growth of lactic acid bacteria growing in milk, butthey did not accele rate the growth in synthetic medium. This lead the authors to suppose that the growth stimulating factors contained in chlorella extracts could be replaced by a suitable mixture of such well-known growth factors as peptides, trace amounts of metals, bases and vitamins, which were inevitable components of synthetic medium. Moreover, the authors discovered that the tolura yeast also had a similar effectf or growth of lactic acid bacteria in milk, and its available factors were readily extractable by water or diluted acids, although their compositions were different from the chlorella extracts in amounts of trace metals.