Strange beauty mesons B(s)0 have been reconstructed through exclusive
hadronic final states, using the data collected in 1992 by the DELPHI
experiment at the LEP collider. The analysis relies on the combined us
e of accurate tracking and of the hadron identification capabilities o
f DELPHI. Three B(s)0 decay candidates have been selected over a negli
gible background using the D(s)- pi+, D(s)- a1+ (1260) and J/ psi phi
decay modes, with identified kaons in the final state. The B(s)0 meson
mass is measured to be m(b)s = (5374 +/- 16 +/- 2) MeV/c2.