BACKGROUND: This paper describes histomorphologic studies on arachnoid granulations in rats, which have not been investigated in China to our knowledge. OBJECTIVE: To observe the distribution of intracranial arachnoid granulations in rats. DESIGN, TIME AND SETTING: The observational experiment was performed in the Academy of Life Sciences of Shandong Taishan Medical College from May to August 2004. MATERIALS: Thirty healthy adult Wistar rats (3-4 months old) of SPF grade, equal numbers of each sex, were selected for this study. Methylene blue parenteral solution was provided by Jiangsu Jichuan Pharmaceutical Company (China), and an optical microscope (Type: CH20; Olympus Co. Ltd., Japan) was used for observation of the histomorphology of the arachnoid granulations. METHOD: Injection of methylene blue parenteral solution into the cerebellomedullary cistern of rats. MAIN OUTCOME MEASURE: The blue stained parts of the lateral sinus were sectioned, stained by hematoxylin and eosin, and then observed under the microscope. RESULTS: The cavitas subarachnoidealis had extensive blue staining after methylene blue injection, while the arachnoid and dura were without dye accumulation. The blue dye indicated the location of the arachnoid granulations. The location of these granulations was fixed, mainly in the lateral sinus at both sides of confluence within 4 mm of the internal jugular vein. CONCLUSION: The arachnoid granulations of the rat were located mainly in the lateral sinuses of the dura mater. BACKGROUND: This paper describes histomorphologic studies on arachnoid granulations in rats, which have not been investigated in China to our knowledge. OBJECTIVE: To observe the distribution of intracranial arachnoid granulations in rats. DESIGN, TIME AND SETTING: The observational experiment was performed in the Academy of Life Sciences of Shandong Taishan Medical College from May to August 2004. MATERIALS: Thirty healthy adult Wistar rats (3-4 months old) of SPF grade, equal numbers of each sex, were selected for this study. Methylene blue parenteral solution was provided by Jiangsu Jichuan Pharmaceutical Company (China), and an optical microscope (Type: CH20; Olympus Co. Ltd., Japan) was used for observation of the histomorphology of the arachnoid granulations. METHOD: Injection of methylene blue parenteral solution into the cerebellomedullary cistern of rats. MAIN OUTCOME MEASURE: The blue stained parts of the lateral sinus were sectioned, stained by hematoxylin and eosin, and the RESULTS: The cavitas subarachnoidealis had extensive blue staining after methylene blue injection, while the arachnoid and dura were without dye accumulation. The blue dye indicates the location of the arachnoid granulations. The location of these granulations was fixed, mainly in the lateral sinus at both sides of confluence within 4 mm of the internal jugular vein. CONCLUSION: The arachnoid granulations of the rat were located mainly in the lateral sinuses of the dura mater.