New precolumn derivatizing reagents for analysis of amino acids by HPLC-butylisothiocyanate (BITC) and benzylisothiocyanate (BZITC)-reacted quantitatively with 22 standard amino acids and the amino acids in the acid hydrolysate of food and protein standard, bovine serum albumin (BSA), at 40 degrees C for 30 min to yield butylthiocarbamyl (BTC) amino acids and at 50 degrees C for 30 min to yield benzylthiocarbammyl (BZTC) amino acids. BTC and BZTC amino acids were successfully separated in 35 min on the reversed-phase Nova-Pak C18 column (30 cm x 3.9 mm, 4 microm). The optimum wavelengths for determination of BTC and BZTC derivatives were 240 nm and 246 nm, respectively. Analysis of the results obtained with BSA and food samples as BTC and BZTC derivatives showed good agreement with those determined as ionexchange chromatography and data presented in the literature. The advantage of BITC reagent over the phenylisothiocyanate (PITC) and BZITC was that it had high volatility, so the excess reagent and by-products were easily removed in about 10 min, compared to about 1 h in the PITC and BZITC reagents. In the BTC and BZTC derivatives, cystine and cysteine were determined separately, but in the PTC amino acids derivatized with PITC reagent they were resolved into single peak.