The permeability of the blood-brain barrier to sodium and albumin was investigated in rats following occlusion of the middle cerebral artery. Regional blood flow and unidirectional transfer coefficients of sodium and albumin were measured by triple tracer autoradiography, and tissue electrolyte content by atomic absorption spectroscopy. In sham-operated controls regional transfer coefficients of sodium ranged between 1.3 and 3.2 x 10(-3) ml.g-1.min-1; the transfer coefficient of albumin was below the detection limit of autoradiography. During the initial 4h of vascular occlusion neither albumin nor sodium permeability changed although tissue sodium content increased from 56 +/- 3 to 76 +/- 8 mumol.g-1. After 24 h transfer coefficient of sodium rose to between 2.91 and 7.0 x 10(-3) ml.g-1.min-1, and tissue sodium content to 90 +/- 9 mumol.g-1. Despite this rise the net uptake rate of sodium was 4 to 60 times lower than the unidirectional influx, indicating that permeability changes of the blood-brain barrier are without relevance for the development of stroke oedema.