The size of the kinetic pool of GTP used in the synthesis of RNA by stage 6 Xenopus laevis oocytes was calculated by expanding the endogenous pool by measured amounts and analysing the incorporation of [3H]GTP into RNA. In experiments on 5 animals, measurements of kinetic pools of GTP ranged from 190.3 to 314.6 pmoles/oocyte and are similar to previously obtained estimates of the chemically extractable GTP pool. Calculations of the rate of stable RNA synthesis ranged from 0.99 to 1.95 pmoles of GTP incorporated per hour per oocyte. These values were also consistent with previous measurements which were based on the assumption that the entire GTP pool provided precursors for stable RNA synthesis. Consequently, it has been concluded that the GTP pool active in RNA synthesis is indistinguishable from the total chemical pool of GTP.