  Supermassive black holes are investigated as possible sources for
low-frequency bursts of gravity waves. The event rate for `known' supermassive
black holes at intermediate and high redshifts, inferred from the quasar
luminosity function, is low $\sim 0.1 \yr^{-1}$. A space-based interferometer
could therefore only see several events per year from supermassive black holes
if an additional population of supermassive black holes existed and emitted
gravitational waves efficiently. These might reside in the population of dwarf
galaxies or in a transient population of small dark matter haloes that have
mostly merged into larger haloes hosting the galaxies seen today. The proposed
space-based gravitational-wave interferometer LISA/SAGITTARIUS should detect
most gravitational-wave events involving supermassive black holes above $10^{4}
\Msol$ out to redshifts of $z \sim 100$.
