The author has investigated the influences of a so-called new vitamin B group comprising orotic acid, thioctic acid, pantothenic acid, adenine, and carnitine at the optimal medium concentrations on the outgrowth of bone marrow cells and motility of neutrophils of normal rat bone marrow cultured in vitro, and obtained the following results. 1. Stimulation of the outgrowth of bone marrow cells was seen with carnitine, adenine, pantothenic acid, thioctic acid, and orotic acid in this declining order. 2. Migrating velocity of bone marrow neutrophils was accelerated with pantothenic acid, adenine, thioctic acid, carnitine, and orotic acid in this declining order.