We use a new redshift survey complete to m _ { R } \simeq 15.4 within 4.25 ^ { o } from the center of the Coma cluster to measure the mass profile of the cluster to r \sim 5.5 h ^ { -1 } Mpc .
We extend the profile to r \sim 10 h ^ { -1 } Mpc with a further sample complete to m _ { R } = 15.4 in 42 % of the area within a 10 ^ { \circ } radius and to m _ { Zw } = 15.5 in the remaining area .
Galaxies within this region are falling onto the cluster on moderately radial orbits and thus do not satisfy virial equilibrium .
Nonetheless , identification of the caustics in redshift space provides an estimate of the gravitational potential at radius r and hence of the system mass , M ( \leq 10 h ^ { -1 } { Mpc } ) = ( 1.65 \pm 0.41 ) \times 10 ^ { 15 } h ^ { -1 } M _ { \odot } ( 1- \sigma error ) .
Previous mass estimates derived from optical and X-ray observations are limited to r \leq 2.5 h ^ { -1 } Mpc .
Our mass profile is consistent with these estimates but extends to distances four times as large .
Over the entire range , the mass increases with r at the rate expected for a Navarro , Frenk & White ( 1997 ) density profile .