Precision measurements of the frequencies of the J=0-->1 transition of HC12N14, HC13N14, DC12N14, and DC13N14 have been made with multiples of a 10-mc/sec. frequency monitored by Station WWV. The B0 and Io values are, respectively: 44300.83 mc and 18.93790 g cm2×10-40 for HC12N14; 43154.83 and 19.44080 for HC13N14; 36207.40 and 23.17108 for HC12N14; 35587.57 and 23.57465 for DC13N14. The interatomic distances determined are dCH=1.061 A and dCN=1.157 A. The nuclear quadrupole coupling of N14 is determined as 4.58+/-0.05 mc/sec.