The aim of the present study was the investigation of haemodynamic changes in the brain in patients after subarachnoid haemorrhage (SAH) using Tc 99 m labelled albumin microspheres (LMS). Twenty-nine patients after SAH (13 in the acute and 16 in the chronic stage of the disease) and four neurologically healthy subjects were examined. LMS were injected in the carotid during angiography and brain and lung scintigrams were taken using gamma camera. In the control subjects a diffuse and uniform distribution of the activity in the brain was found. In the patients with acute SAH "patchy", nonhomogenous distribution of the activity was found, ranging up to the regional absence of perfusion. This pattern was observed in the chronic stage as well, but less obvious than in the acute. In all the patients the evident trapping of LMS in the lungs was demonstrated confirming brain shunts, absent in the control group. By measuring the activity in the brain and lungs after intracarotid injection of LMS, haemodynamic changes in the patients after SAH were proved and the existence of brain shunts was demonstrated. It seems that shunts are functional anastomoses and important protective mechanism, opening when cerebral haemodynamics is altered.