Prostaglandin F2α-d4 (PGF2α-d4) contains four deuterium atoms at the 3, 3', 4, and 4' positions. It is intended for use as an internal standard for the quantification of PGF2α by GC- or LC-mass spectrometry. PGF2α is a widely distributed prostaglandin occurring in many species. It causes contraction of vascular, bronchial, intestinal, and myometrial smooth muscle, and also exerts potent luteolytic activity. PGF2α exhibits its receptor mediated physiological activity at 50-100 nM. Maximal ovine myometrial contraction can be achieved at 125 nM PGF2α in vitro.