We have searched for the flavor-changing neutral current decay b --> X
-s mu(+)mu(-) in <p(p)over bar> collisions at root s = 1.8 TeV with th
e D0 detector at Fermilab. We determine the 90% confidence level limit
for the branching fraction to be B(b --> X-S mu(+)mu(-)) < 3.2 X 10(-
4). We argue that this limit is more stringent than the best published
limit on this decay rate. (C) 1998 Elsevier Science B.V.