A completely electronic sweep spectroscope of high resolution has been developed for the wave-length region from 2 to 3 millimeters (150,000 mc/sec. to 100,000 mc/sec.). The radiation source is a silicon crystal harmonic generator driven by Ratheon klystrons. Silicon crystals are used also as detectors. Radiation of wave-length 1.96 mm (154,000 mc/sec.) has been generated and detected with strength more than ten times the noise level. Some lines in the hyperfine structure of the J=19-->20 rotational transition of ICN at 2.32 mm have been observed. The J=1-->2 transition of CH3F has been observed at 2.93, and the separation of the K=1 and K=0 lines has been determined as 1.8 mc. Precision measurements on the first rotational line (J=0-->1) of C12O16, and C13O16 in the 2.6-mm region have been made with an electronic frequency standard monitored by the 10 mc/sec. signal of station WWV. The following molecular constants were determined: for C12O16, B0=1.922625 cm-1, Be=1.931367 cm-1, I0=14.55531×10-40 g cm2, Ie=14.48943×10-40 g cm2, r0=1.130789A, re=1.128227A; for C13O16 B0=1.838069 cm-1, I0=15.22489×10-40 g cm2, r0=1.130725A. The last three digits quoted for r and I have relative significance only, because of possible error in Planck's constant.