Phase 1a is an open-label, multi-dose, single-arm, dose-escalation study to define the toxicity profile, pharmacokinetics, and antitumor activity of SGN-33 in patients with myelodysplastic syndrome (MDS), acute myelogenous leukemia(AML), and CD33+ myeloproliferative diseases. Phase 1b includes patients with AML or MDS treated at the highest tolerated dose from phase 1a.