  We study the conformational properties of heteropolymers containing two types
of monomers A and B, modeled as self-avoiding random walks on a regular
lattice. Such a model can describe in particular the sequences of hydrophobic
and hydrophilic residues in proteins (K.F. Lau and K.A. Dill, Macromolecules
{\bf 22}, 3986 (1989)) and polyampholytes with oppositely charged groups (Y.
Kantor and M. Kardar, Europhys. Lett.{\bf 28}, 169 (1994)). Treating the
sequences of the two types of monomers as quenched random variables, we provide
a systematic analysis of possible generalizations of this model. To this end we
apply the pruned-enriched Rosenbluth chain-growth algorithm (PERM), which
allows us to obtain the phase diagrams of extended and compact states
coexistence as function of both the temperature and fraction of A and B
monomers along the heteropolymer chain.
