We have performed a search for B0(s) --> mu+ mu- and B0
--> mu+ mu- decays in p anti-p collisions at s**(1/2) = 1.96 TeV
using 2 fb-1 of integrated luminosity collected by the CDF II detector
at the Fermilab Tevatron Collider. The observed number of B0(s) and B0
candidates is consistent with background expectations. The resulting
upper limits on the branching fractions are B(B0(s) --> mu+ mu-) <
5.8 x 10-8 and B(B0 --> mu+ mu-) < 1.8 x 10-8 at 95% C.L.