Furoin, a benzoin analogue, was examined as novel fluorogenic reagent for the selective and sensitive LC determination of various guanidines after pre-column derivatization. The derivatization reaction was carried out at 100 degrees C for 5 min to give adducts that were separated on a Phenomenex Synergi MAX-RP column and detected at lambda(em)=410 nm with lambda(ex)=325 nm. The reagent showed to be useful both for determining together arginine (Arg) and creatine (CT) in dietary supplements under elution isocratic conditions and for the simultaneous analysis of a variety of guanidines in biological samples (human plasma and urine) under elution gradient conditions. The detection limits ranged from 7 to 25 fmol. Recovery studies showed good results for all determined guanidino compounds (85.6-106.2%; R.S.D.=1.1-6.2%).