The blood-brain barrier (BBB) arises from epithelial-like tight junctions that virtually cement adjoining capillary endothelium together in the brain microvasculature. Several experimental manipulations have been shown able to increase the permeability of brain capillaries, by altering endothelial cell membrane integrity or activating specific biochemical pathways involved in regulation of BBB functionality. Because of its amphiphilic nature, sodium dodecyl sulphate (an anionic surfactant widely used as solubilizer or stabilizer in several pharmaceutical preparations; SDS) may enter into interactions with the major membrane components, which are lipids and proteins. The aim of the present study was to determine the effect of an intracarotid infusion of SDS (25, 50 and 100 microg/kg; infusion rate: 3 ml/min for 30 s) on the functionality of the BBB in the rat. An extensive, dose-dependent Evans blue extravasation was observed, in the ipsilateral brain hemisphere, 15 min following SDS infusion. These results were confirmed by the significant increase in [14C]alpha-aminoisobutyric acid ([14C]AIB) transport (evaluated by calculating a unidirectional transfer constant, Ki, for the tracer from blood to brain) measured in several ipsilateral brain regions 2 min after SDS infusion; this SDS-elicited BBB opening to [14C]AIB proved to be reversible. Since the BBB is created by the plasma membrane and tight junctions of the endothelial cells, the change in BBB permeability caused by SDS might be explained as a nonspecific surfactant-membrane interaction. Furthermore, SDS might affect the functional characteristics of brain vascular endothelial cells by an interaction with specific BBB proteins and/or biochemical pathways. In conclusion, one can suggest that intracarotid infusion of SDS might provide a useful clinical approach for the intentional introduction of different substances into the brain. On the other hand, these findings should call attention to possible dangerous consequences of using SDS as solubilizer in drug excipients.