This letter reports the observation and mass measurement of
fully reconstructed Bs mesons through the decay chain Bs -> J/psi phi,
J/psi -> mu+ mu-, phi -> K+ K- using data obtained at the Collider
Detector at Fermilab in p p-bar collisions at sqrt{s} = 1.8 TeV.
A signal of 14.0 +- 4.7 events is observed.  Comparison of the Bs 
signal with the kinematically similar decays B+ -> J/psi K+ and 
B0 -> J/psi K* is presented.  The mass of the Bs meson is determined to
be 5383.3 +- 4.5 (stat) +- 5.0 (syst) MeV/c**2.