Razoxane (100 mg/kg) was administered to rats as a single IP dose. Plasma and CSF samples were obtained at intervals varying from 15 min to 24 h after dosing, and the razoxane was assayed by a new and simple high performance liquid chromatography (HPLC) technique. Razoxane was absorbed quickly from the peritoneal cavity; it reached a peak concentration within 0.5 h and decayed with a half-life of 1.6 h. Only 10% of the plasma razoxane available entered the CSF, reaching a peak concentration by 2h, which was maintained for a further 4 h, and finally decaying to reach 10% of its peak value by 8 h.