ABSTRACTA new synthetic medium was developed for the production of submerged mycelial cultures ofLentinus edodes.Glucose and ammonium chloride were the best carbon and nitrogen sources, respectively. The remaining ingredients in the medium were calcium chloride, aspartic acid, thiamine, magnesium sulphate and trace elements (Mn, Zn and Fe). The threshold level in the dry weight of mycelium was reached at an inoculum concentration of 9.9 mg/ml and was maintained through 16.5 mg/ml. The size of mycelial pellet was inversely related to the level of inoculum. Similar relationships were obtained between mycelial growth and mycelial pellet and shaking frequencies from 50–200 rpm. Optimum growth occurred at pH 4.3-4.8 and at temperatures 20–25 C. Mycelial growth in the new synthetic medium was increased five-fold by using an airlift fermentor instead of shaking. The number of days to the appearance of the first flush of sporophores was reduced by 45 da by using liquid spawn. An important difference between the ultrastructure of cells of the agar-grown filamentous hyphae and those of mycelial pellets in submerged culture is that paramural bodies were prominent in the former.