Our purpose was to assess the haemodynamic changes in the ipsilateral middle cerebral artery (MCA) during and after percutaneous transluminal angioplasty (PTA) of the internal carotid artery (ICA), and to compare them with clinical and angiographic findings. Transcranial Doppler Sonographic monitoring (TCD) of the MCA was performed during PTA in 22 patients with symptomatic severe stenosis of the ICA. Mean blood flow velocity (MBFV) and pulsatility index (PI) were recorded. During PTA, MBFV fell from 41 +/- 15 cm/s to 23 +/- 11 cm/s (P = 0.0001). Changes in PI were inconsistent. With reduction of MBFV of 50% or less (in 10 cases) no complication occurred. With a reduction of more than 50% (in 12), 6 patients developed neurological disturbances (transient ischaemic attacks in 5 and minor stroke in 1). This difference was significant (P = 0.0152). Symptomatic patients also had a higher rate of stroke prior to PTA (4/6) than patients who remained asymptomatic during PTA (0/6). After PTA had been performed MBFV and PI improved significantly (P = 0.0001), MBFV increasing to 48 +/- 16 cm/s and PI from 0.64 +/- 0.11 to 0.86 +/- 0.15. TCD changes proved more sensitive to cerebral haemodynamics than angiography in 8 patients.