A sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for determining the type B fumonisin mycotoxins in corn-based foodstuffs is described. Fumonisins FB1 and FB2 were extracted from a 1 g sample by homogenization with acetonitrile/water (75:25, v/v, 50 mmol/L formic acid, 25 mL final volume) and the extract was defatted on C18 phase. Volumes of 5 mL of crude extracts were cleaned up on Carbograph-4 cartridges. The final solution was analyzed by HPLC with electrospray ionization mass spectrometry in positive ion mode using multiple reaction monitoring with a QqQ linear ion trap mass spectrometer. Recoveries for spiked corn-based foodstuffs ranged from 91-105% (RSD% < or =8%), and method detection limits were < or =2 ng/g for FB1 and < or =1 ng/g for FB2. Two different spiking levels were tested (5000 and 100 ng/g for FB1, 1000 and 20 ng/g for FB2). Quantitation was achieved by an external calibration procedure using matrix-matched standards, with diclofenac added post-cleanup as internal standard for the LC/MS/MS analyses. Calibration curves showed linearity in the concentration range 0.005-5 ng/microL of final extract (0.992 < or = R2< or =0.995). Two other fumonisins, FB3 and FB4, were identified in naturally contaminated samples of corn meal using an information-dependent acquisition protocol that looped three experiments, including neutral loss scan, enhanced resolution scan, and enhanced product ion scan. FB3 and FB4 quantitation was estimated as peak area ratios relative to the FB2 response in view of the lack of both standards. This work also includes an application of the present LC/MS/MS method to some maize and maize-based product samples (corn meal, cornflakes and popcorn) collected from Italian stores. FB1 and FB2 contamination levels exceeding the European Union recommendation were found in 8 out of 15 corn meal samples.