1. The importance of migraine equivalents has been indicated with regard to problems of diagnosis in medicine and to the understanding of the nature of migraine.2. Equivalents may replace migraine entirely and be episodic or continued in form, or may alternate with migraine attacks in episodic form.3. In a series of 169 migrainous patients, equivalents occurred in 30.8 per cent over the period of observation.4. The equivalents lend support to the theory that migraine is the result of an imbalance between processes of excitation and capacities for external "discharge." Whereas the former is dependent on constitutional factors, the latter is determined largely by factors of training and experience affecting the organization of the nervous system.5. Equivalents occur in migraine in relation to alterations in intensity of the nervous processes involved, as dependent on external factors of stress or to changes in the affector-effector balance.6. The specific form of some equivalents is presumably dependent on constitutional factors.Abstract Teaser