Recent advances in fast magnetic resonance imaging (MRI) techniques have allowed quantification of parameters such as T1 relaxation time, which can be modified by changes in the water content of a tissue. We have used this new method to study the evolution of blood-brain barrier (BBB) changes after adoptive transfer of MBP-specific (AT-EAE) and ovalbumin-specific T cell lines in Lewis rats. Measurable changes in T1 relaxation time suggesting widespread increase in BBB permeability were found, starting on day 3 post inoculation (p.i.), in the midbrain and brainstem of AT-EAE rats. In addition, we noted a significant decrease in T1 relaxation time before injection of a paramagnetic agent, in the cisternal cerebrospinal fluid (CSF) of diseased animals, starting on day 5 p.i. In vitro measurement of T1 in CSF containing various concentrations of albumin, IgM and glucose showed that, at physiological concentrations, a T1 decrease is mainly associated with an increase in albumin concentration. A moderate increase in BBB and blood-CSF barrier permeability was found as early as 4-8 h p.i., in rats injected with MBP-specific as in animals injected with ovalbumin-specific T cell lines, suggesting a non-specific mechanism. Experimental MRI may become a powerful tool to sequentially analyse changes in barrier dynamics, for example following pharmacological intervention.