Attempts to characterize the mechanism(s) associated with myoclonus have led to the development of several naturally occurring and pharmacologically based animal models of myoclonus. Congenital disorders in animals that result in myoclonic seizures have been found in subpopulations of baboons that exhibit photoresponsive myoclonus and in herds of Hereford cattle that possess a fatal, autosomal-inherited imbalance in spinal glycine neurotransmission. Pharmacologically based models of myoclonus use a variety of approaches to product myoclonic seizures in test animals.