Technical Abstract: A high performance liquid chromatographic (HPLC) method for determination of vanillan in boiled peanuts has been developed. Vanillan was extracted with acetonitrile by blending at high speed followed by purification of an aliquot of the extract on a minicolumn packed with aluminum oxide. Vanillan was quantitated by HPLC on silica gel with n-hexane-2-propanol-water-acetic cacid (2100+540+37+2,v/v) as a mobile phase. The recovery of vanillin added to fresh peanut hulls at .50 and 2.50 ug/g was 78.7 +/- 2.7 and 79.9 +/- 3.1%, respectively. The detection limit of vanillan in boiled peanuts was estimated at 0.05 ug/g. UV-detector response to vanillan was linear to at least 2.5 ug/injection. Free vanillan has been found in two commercial brands of boiled peanuts at low ppm levels. Both the kernels and the hulls contained vanillan, which was formed during hydrolysis of lignin, one of the major constituents of the peanut hulls. Since vanillin has a low flavor threshold, it could be considered as one of the major ingredients that determine the flavor of boiled peanuts.