Long-duration gamma-ray bursts are the manifestations of massive stellar
death. Due to the immense energy release they are detectable from most of the
observable universe. In this way they allow us to study the deaths of single
(or binary) massive stars possibly throughout the full timespan massive stars
have existed in the Universe. GRBs provide a means to infer information about
the environments and typical galaxies in which massive stars are formed. Two
main obstacles remain to be crossed before the full potential of GRBs as probes
of massive stars can be harvested: i) we need to build more complete and well
understood samples in order not to be fooled by biases, and ii) we need to
understand to which extent GRBs may be intrinsically biased in the sense that
they are only formed by a limited subset of massive stars defined by most
likely a restricted metallicity interval. We describe the status of an ongoing
effort to build a more complete sample of long-duration GRBs with measured
redshifts. Already now we can conclude that the environments of GRB progenitors
are very diverse with metallicities ranging from solar to a hundredth solar and
extinction ranging from none to A_V>5 mag. We have also identified a sightline
with significant escape of Lyman continuum photons and another with a clear
2175AA extinction bump.Comment: Invited review - in "Massive Stars as Cosmic Engines", IAU Symp. 250
(Kauai), ed. F. Bresolin, P. A. Crowther, and J. Puls (Cambridge University
Press), p. 443-456. Typos and refs correcte
