Immature mulberry leaves isolated from winter buds were cultured on MS media7) differing in the nitrogen source, sugar(s) or pH, or containing various kinds and concentrations of plant hormones, antibiotics or a herbicide. The ratio of the concentration of nitrate ion to that of ammonium ion remarkably affected the frequency of adventitious bud formation (FABF) and ratios in the ranges of 1:1 and 3:1 were optimum. The most suitable sugars for adventitious bud formation were sucrose, glucose and fructose among the tested sugars. The highest FABF was usually observed in the medium containing 1 μM thidiazuron and the addition of 1 μM abscisic acid further enhanced FABF. Changes of pH and addition of other plant hormones did not produce better results than in the control. Kanamycin, geneticin, hygromycin and bialaphos suppressed adventitious bud formation, showing that the antibiotics and the herbicide may be effective for the selection of transgenic plantlets of mulberry.