The growth of Frankia cells within alginate beads was inhibited when the amount encapsulated exceeded o.5 to 2.5 microg protein/ml of beads. Frankia growth was observed not only in the beads incubated in nutrient media (with or without combined N), but also in those incubated in air provided they retained enough nutrients. The results allow some recommendations to be made for the preparation of Frankia inoculants.