We have assembled 21-cm linewidths for 376 of the 732 galaxies in a magnitude-limited redshift survey of the Perseus-Pisces region .

We analyze a distance limited subset of 271 galaxies ( 131 widths ) to examine the relationship between linewidth and local density .
The sample indicates that galaxies with linewidths \gtrsim 480 km/s are absent from regions where the galaxy density is \lesssim 0.03 galaxies Mpc ^ { -3 } ( M _ { B ( 0 ) } < -18.3 ) .
This effect is in the direction predicted by standard CDM models .
Galaxies with linewidths \lesssim 480 km/s appear throughout the sample .

The observational constraints could be susbtantially improved with a larger sample , IR photometry , and more uniform 21-cm data .