  We present experimental results on the two-body loss rates in a
magneto-optical trap of metastable helium atoms. Absolute rates are measured in
a systematic way for several laser detunings ranging from -5 to -30 MHz and at
different intensities, by monitoring the decay of the trap fluorescence. The
dependence of the two-body loss rate coefficient $\beta$ on the excited state
($2^3P_2$) and metastable state ($2^3S_1$) populations is also investigated.
  From these results we infer a rather uniform rate constant
$K_{sp}=(1{\pm}0.4)\times10^{-7}$ cm$^3$/s.
