The light curve of the outburst of Comet P/Metcalf-Brewington (1991 1)
is investigated. The parameters of the light curve are quite uncertai
n as it may be fitted both in terms of variation with heliocentric dis
tance and exponential decay with time however, after maximum a empiric
al fit of m1 = 4.1 + 5 log Delta + 14.8 log r gives a good fit to the
data. The absolute magnitude brightened at least 11 magnitudes in outb
urst. The outburst is most plausibly caused by the release of micron s
ized grains as, were the outbust due to dust emission, it would imply
the expulsion of a large fraction of the total mass of the nucleus.