The synchronization of MR data collection with respiration is essential for collecting high‐quality, in vivo magnetic resonance images and spectra of rodents. In this article, we describe the design and operation of a simple, robust device for respiratory gating. Inexpensive and easy to construct, the device operates in either free‐breathing or actively driven (ventilator) modes. Respiration is monitored either by a pressure transducer connected to the nosecone used to deliver anesthesia to the animal or by a fiber‐optic detector of the animal's motion. The device generates a TTL signal that can be used to trigger the MR scanner to enable respiratory‐synchronized data acquisition. A variety of different MR imaging sequences can be easily modified to incorporate respiratory gating. We present respiratory‐synchronized imaging and spectroscopy results obtained using this device, including ¹H MR images of mouse lung, liver, and spinal cord and localized ¹H spectra of mouse liver. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 21B: 40–48, 2004