By the simultaneous detection of the p, T, and He3 particles in a thin window proportional counter the concurrent nuclear reactions D(d,p)T and D(d,n)He3 have been investigated throughout the deuteron energy range 26 to 63 kev. The ratio of the yield of the reaction D(d,p)T to that of the reaction D(d,n)He3 was found to be 1.15 ± 0.15 throughout this energy range. There is some slight evidence for an increase in this ratio towards lower bombarding energies.