Emission from SO towards a number of HII regions and molecular clouds with embedded energy sources has been reported by several authors (e.g., Gottlieb et al. 1978; Clark et al. 1978; Wannier and Phillips 1977; and references therein; cf. also Loren et al., 1974; Loren et al. 1975; Lada et al. 1974). Transitions observed include the 45→44, 43→32, 32→21, 23→12, 22→11, 12→11, and 10→01, with the latter (to the ground state) seen only in Sgr B2. Recently Rydbeck et al. (1980) have detected SO in cold, dark clouds and have made the first astronomical measurements of the 10→01 transition in a variety of sources, including the corresponding 34SO line. The latter authors find that the 10→01 transition of SO is an excellent tracer of structure in dark clouds, and they discuss the fractional abundance [SO]/[H2] on the basis of column densities derived from observations of the two isotopic species. They also set limits to the magnetic field strength in dark clouds from the absence of observed Zeeman splitting. We shall provide here additional spectra and information on observing procedures, and shall discuss the rest frequencies for the SO and 34SO 10→01 transitions.