  We present 37 GHz data obtained at Metsahovi Radio Observatory in 2001
December - 2005 April for a large sample of BL Lacertae objects. We also report
the mean variability indices and radio spectral indices in frequency intervals
5 - 37 GHz and 37 - 90 GHz. Approximately 34 % of the sample was detected at 37
GHz, 136 BL Lacertae objects in all. A large majority of the detected sources
were low-energy BL Lacs (LBLs). The variability index values of the sample were
diverse, the mean fractional variability of the sample being \Delta S_2 = 0.31.
The spectral indices also varied widely, but the average radio spectrum of the
sample sources is flat. Our observations show that many of the high-energy BL
Lacs (HBL), which are usually considered radio-quiet, can at times be detected
at 37 GHz.
