We developed a simple quantitative procedure for cholestanol in serum involving reversed phase thin layer chromatography. This procedure was satisfactory with regard to the linearity of the calibration curve in the range of 100 ng to 1,000 ng, recovery and reproducibility. Only 100 microliter of serum was needed for determination of the cholestanol concentration. Prior to thin layer chromatography, cholesterol was converted to alpha- and beta-epoxides with m-chloroperbenzoic acid, which were clearly distinguishable from cholestanol on TLC. Detection of sterols was performed by spraying with phosphomolybdic acid solution. Quantification of cholestanol was carried out with a TLC scanning densitometer. When serum cholestanol in cerebrotendinous xanthomatosis (CTX) patients was quantified by TLC, GC-MS, and GC, the correlation among the three methods was found to be approximately 1:1:1. It was found that the present method was useful for the primary diagnostic screening of CTX because of its simplicity and because many samples could be analyzed at one time.