Two patients with SUNCT syndrome (short-lasting, unilateral, neuralgiform headache attacks with conjunctival injection and tearing) were investigated. Blood flow velocity in the middle cerebral artery was monitored before, during, and outside four spontaneous attacks. An interhemispheric asymmetry was observed. In the second case, velocity decreased significantly on both sides during attacks in comparison with preattack values, Cerebral SPECT (single photon emission computed tomography) images were obtained during a bout and between attacks in one patient. The radiocompound was injected 5 to 10 seconds after the start of an attack. In both patients, normal tracer uptake and symmetric perfusion was observed during headache periods.