  A search has been made for 21 cm HI line emission in a total of 350 unique
galaxies from two samples whose optical properties indicate they may be massive
The first consists of 241 low surface brightness (LSB) galaxies of
morphological type Sb and later selected from the HyperLeda database and the
the second consists of 119 LSB galaxies from the UGC with morphological types
Sd-m and later. Of the 350 unique galaxies, 239 were observed at the Nancay
Radio Telescope, 161 at the Green Bank Telescope, and 66 at the Arecibo
telescope. A total of 295 (84.3%) were detected, of which 253 (72.3%) appear to
be uncontaminated by any other galaxies within the telescope beam. Finally, of
the total detected, uncontaminated galaxies, at least 31 appear to be massive
LSB galaxies, with a total HI mass $\ge$ 10$^{10}$ M$_{sol}$, for H$_0$ = 70
km/s/Mpc. If we expand the definition to also include galaxies with significant
total (rather than just gas) mass, i.e., those with inclination-corrected HI
line width W$_{50}$,cor > 500 km/s, this bring the total number of massive LSB
galaxies to 41. There are no obvious trends between the various measured global
galaxy properties, particularly between mean surface brightness and galaxy
mass.
