We present the results of prominence observations at RT-22 CrAO in April, May, and September 1993 at 13.5 mm (intensity and circular polarization) and at 8.2 mm (intensity) wavelengths carried out by circular scanning using the combined scalar horn. On the assumption of thermal cyclotron radiation we have measured the values of the longitudinal component of the magnetic field for 18 prominences. The histogram of the distribution of the longitudinal component indicates the presence of maxima in the vicinity of 8, 15, and 25– 30 G. Our results are compared with the distributions obtained from optical measurements.