A conjecture due to Gompf asserts that no nontrivial Brieskorn homology sphere admits a pseudoconvex embedding in C 2 , with either orientation. A related question asks whether every compact contractible 4-manifold admits the structure of a Stein domain. We verify Gompf's conjecture, with one orientation, for a family of Brieskorn spheres of which some are known to admit a smooth embedding in C 2 . With the other orientation our methods do not resolve the question, but do give rise to an example of a contractible, boundaryirreducible 4-manifold that admits no Stein structure with either orientation, though its boundary has Stein fillings with both orientations.