The National Institute of Neurological Disorders and Stroke (NINDS), the National Institute on Aging (NIA), the National Heart, Lung, and Blood Institute (NHLBI), and the National Institute of Arthritis and Skin Diseases (NIAMS) encourage investigator-initiated research grant applications to study restless legs syndrome and periodic limb movement disorder. Restless legs syndrome (RLS) is a disorder characterized by disagreeable leg sensations, usually prior to sleep onset, that cause an almost irresistible urge to move the legs. Periodic limb movement disorder is characterized by periodic episodes of repetitive and highly stereotyped limb movements that occur during sleep. Although the term, periodic limb movement disorder, is preferred, this disorder is also referred to as periodic leg movements (PLMs), nocturnal myoclonus, periodic movements in sleep (PMS), and leg jerks. The overwhelming majority of patients with RLS also have periodic limb movement disorder. This announcement re-issues PA-01-086. The previous announcement was released in May, 2001 and led to the funding of RLS research discoveries in several important areas including links between RLS and dopamine/motor systems and/or iron transport mechanisms. RLS is a common neurological disorder affecting up to 11% of adults. Sensory symptoms are intensified by time of day (evening), inactivity and lying down. These symptoms lead to difficulty falling asleep and staying asleep. Left untreated, RLS causes exhaustion and fatigue, which can affect work and socio-familial activities. Both RLS and periodic limb movement disorder occur in a substantial fraction of patients suffering from Parkinson's disease and narcolepsy, two other disorders thought to involve central dopamine mechanism. This PA is intended to expand RLS research as well as build upon already funded work addressing the hypotheses that acquired or genetically mediated dysfunctions in dopamine/motor systems and/or iron transport mechanisms are etiologically linked to RLS symptoms. Of particular relevance to this PA are applications that address the sensory gating and circadian timing aspects of RLS which are defining features of the condition.