The dynamic behaviour of the distribution of Evans blue (EB), sodium fluorescein (SF), Lucifer yellow (LY) and horseradish peroxidase (HRP) was studied using standard light- and fluorescence microscopy following ultraviolet radiation induced brain oedema in the rat model. The cerebral cortex was irradiated after craniotomy (2 x 2 mm) under anaesthesia. The tracers were injected (iv) 30 min prior to radiation. Animals were perfused with glutaraldehyde through the heart at different survival periods ranging from 30 min to 24 h post irradiation. The results showed a remarkable difference in distribution and spread of these tracers in the oedematous brain following radiation. The extravasation of EB was evident in ipsilateral cortex 6 h after radiation which extended to the contralateral side at the end of the 24 h survival period. The HRP reaction product was seen in the necrotic area 3 h after radiation which further extended to the underlying white matter at 24 h survival. The LY stained the ipsilateral micronecrotic area 6 h after radiation, whereas a non-specific diffuse fluorescence of SF was noted at this time period. These results point out a specific selectivity of tracer distribution in oedematous brain following ultraviolet radiation.