  We study a sample of bright long BATSE GRB light curves in the 200 s before
the detection of the GRB prompt emission. We find that in a sizable fraction of
cases (20 %) there is evidence of emission above the background coming from the
same direction of the GRB. This emission is characterised by a softer spectrum
with respect to the main one and contains a small fraction (0.1-1 %) of the
total event counts. The precursors have typical delays of several tens of
seconds extending (in few cases) up to 200 seconds (the limit of the
investigated period). Their spectra are typically non-thermal power-law but for
a few cases. Such long delays and the non-thermal origin of their spectra are
hard to reconcile with any model for the progenitor.
