The hydrochloride salt of an orally-active thiazolidinedione with antidiabetic properties and potential antineoplastic activity. Pioglitazone activates peroxisome proliferator-activated receptor gamma (PPAR-gamma), a ligand-activated transcription factor, thereby inducing cell differentiation and inhibiting cell growth and angiogenesis. This agent also modulates the transcription of insulin-responsive genes, inhibits macrophage and monocyte activation, and stimulates adipocyte differentiation.