The descriptive term ultradian is used in sleep research in reference to the 90–120 minute cycling of the sleep stages during human sleep.

Some of the other ultradian cyclings of the body are hormonal release, heart rate, thermoregulation, urination, bowel activity, nostril dilation and appetite. The last involves rhythmic release of Neuropeptide Y (NPY) and Corticotropin-releasing hormone (CRH), stimulating and inhibiting appetite ultradian rhythms.

Caenorhabditis elegans is often used as a model animal for ultradian rhythm. Defecation in C. elegans is a tightly controlled rhythmic process. Posterior body wall muscle contractions in C. elegans occur rhythmically every 45–50 seconds and mediate defecation.

Ultradian states in bipolar disorder cycle much faster than rapid cycling, which is defined as four or more mood episodes in one year, sometimes occurring within a few weeks.a Ultradian mood cycling is characterized by cycles shorter than 24 hours.