Eyes are supplied O-2 through the cornea and vessels of the retina and iris, which are tissues characterized by aerobic metabolism. Meanwhile, there are no reports on the association between iris sphincter contraction and aerobic metabolism. In this paper, we studied the aforementioned association. Eyes from adult pigs of either sex were obtained from a local abattoir. A muscle strip was connected to a transducer to isometrically record the tension. O-2 consumption was measured using a Clark-type polarograph connected to a biological oxygen monitor. Creatine phosphate (PCr) and adenosine triphosphate (ATP) contents were measured in the muscle strips by high-performance liquid chromatography (HPLC). Iris sphincter muscles were measured in resting, contractile or hypoxic phases. Contraction was induced by hyperosmotic 65 mM KCl (H-65K(+)) or carbachol (CCh), and hypoxia was induced by aeration with N-2 instead of O-2 or by addition of sodium cyanide (NaCN). H-65K(+)- and CCh-induced muscle contraction, involved increasing O-2 consumption. Hypoxia and NaCN significantly decreased H-65K(+)- and CCh-induced muscle contraction and/or O-2 consumption and PCr contents. Our results suggest that the contractile behavior in porcine iris sphincter highly depends on mitogen oxidative metabolism.