The endothelin-1 (ET-1) gene was disrupted in mouse embryonic stem cells by homologous recombination to generate mice deficient in ET-1. These ET-1-/- homozygous mice die of respiratory failure at birth and have morphological abnormalities of the pharyngeal-arch-derived craniofacial tissues and organs. ET-1+/- heterozygous mice, which produce lower levels of ET-1 than wild-type mice, develop elevated blood pressure. These results suggest that ET-1 is essential for normal mouse development and may also play a physiological role in cardiovascular homeostasis.