Nuclear fission of uranium and thorium under bombardment by deuterons of about 9 MeV has been investigated both qualitatively and quantitatively by the use of the 'active-deposit' technique. The following results have been obtained: (i) The range of the fission fragments from both uranium and thorium is about 2$\cdot $3 cm. in air. (ii) The decay curve agrees in scale and shape with that which would be expected from a complex mixture of radioactive bodies. (iii) The active deposit has been examined for emission of $\beta $-rays, positrons, $\gamma $- and X-rays, $\alpha $-particles and neutrons; the radiations are found to bear a general similarity to those resulting from neutron-induced fission. (iv) Some of the radioactive bodies have been isolated by chemical methods; some correspondence with the products of neutron-induced fission is shown. (v) The ratio of the fission cross-sections for 9 MeV deuterons and (Li + D) neutrons has been measured. (vi) The excitation function has been studied. The experimental data from (v) and (vi) are compared with calculations based on Bohr and Wheeler's treatment of the mechanism of the process.