  Measurements of on-shell ZZ production are described, using data collected by
DELPHI in 1997 and 1998, at centre-of-mass energies sqrt(s) = 182.6 GeV and
188.6 GeV respectively. Results obtained in each of the final states q qbar q
qbar, mu+mu- q qbar, e+e- q qbar, nu nubar q qbar, l+l-l+l-, and nu nubar l+l-
are presented. The measured cross-sections for on-shell ZZ production via the
tree-level doubly-resonant graphs (NC02) are: sigma_{NC02}(182.6 GeV) = 0.38 +-
0.18 (stat) +- 0.04 (syst) pb, sigma_{NC02}(188.6 GeV) = 0.60 +- 0.13 (stat) +-
0.07 (syst) pb. They are consistent with the Standard Model expectations of
0.25 pb and 0.65 pb at each energy.
