A sensitive and selective analytical method was developed for the quantitative determination of fumonisins B(1) and B(2) in maize-based foods for direct human consumption. The method, based on high-performance liquid chromatography and fluorescence detection, presents a rapid and automated on-line post-column derivatization, performed with o-phtalaldehyde and N,N-dimethyl-2-mercaptoethylamine. Several factors affecting the separation and detection of fumonisins were investigated, including mobile phase composition, column features, derivatization agent flow-rate and both the excitation and the emission wavelengths. Optimal fluorescence detection was obtained by using a lambda(exc) of 343 nm and a lambda(em) of 445 nm. Under the optimized experimental conditions, a complete separation of fumonisins was obtained in less than 13 min by using a C(18) column and a gradient elution at 0.8 mL/min with methanol and 0.1M phosphate buffer at pH 3.15. The limits of detection for FB(1) and FB(2) were 4 and 5 microg/L corresponding to 5 and 6 microg/kg in matrix. Each fumonisin was determined in the range 40-320 microg/L that correspond to 50-400 microg/kg in matrix. The necessary requirements for accuracy, reproducibility and sensitivity were fulfilled and recovery values ranged from 87 to 94% for FB(1) and from 70 to 75% for FB(2) in cornflake samples at three fortification levels in the range 100-300 microg/kg. The potential of this method, combined with a simple clean-up procedure, was assessed by the measurements of FB(1) and FB(2) in maize-based products, such as maize flour, "polenta", tortillas and cookies.