This paper describes topological searches for neutral
scalar bosons $\rm S^0$ produced in association with a $\rm Z^0$ boson
via the Bjorken process $\rm e^+e^-\rightarrow S^0Z^0$ at centre-of-mass
energies of 91\,GeV and 183--209\,GeV.  These searches are based
on studies of the recoil mass spectrum of $\rm Z^0\rightarrow e^+e^-$ and
$\mu^+ \mu^-$ events and on a search for $\rm S^0Z^0$ with
$\rm Z^0\rightarrow \nu\bar{\nu}$ and $\rm S^0 \rightarrow e^+e^-$ 
or photons.  They
cover the decays of the $\rm S^0$ into an arbitrary combination of
hadrons, leptons, photons and invisible particles as well as the
possibility that it might be stable.
  
No indication for a signal is found in the data and upper limits
on the cross-section of the Bjorken process are calculated.
Cross-section limits are given in terms of a scale factor $k$
with respect to the Standard Model cross-section for the Higgs-strahlung
process $\rm e^+e^-\rightarrow H^0_{SM}Z^0$.
  
These results can be interpreted in general scenarios
independently of the decay modes of the $\rm S^0$. The examples
considered here are the production of a single new scalar particle
with a decay width smaller than the detector mass resolution, and
for the first time, two scenarios with continuous mass
distributions, due to a single very broad state or several states
close in mass.