Carmustine and fotemustine were perfused using a bolus retrograde infusion into the right external carotid artery of rats. The right jugular vein gave blood samples. Using a previously described method, nitrosoureas were continuously measured in rat brain by voltammetry and in blood samples by high-performance liquid chromatography for 15 min. Cerebrovascular permeability coefficients calculated in the first 2 min were 0.9.10(-4) cm.s-1 for carmustine and 0.5.10(-4) cm.s-1 for fotemustine. These high brain permeability coefficients were compared to literature values for carmustine and other nitrosoureas determined with a radioactive procedure.