Triacylglycerols of 50 samples of subcutaneous fat of Iberian pigs reared extensively on two different feeding systems: montanera (M) and cebo (C) have been analysed by gas chromatography flame ionization detector. The lipids were extracted by melting from subcutaneous fat into microwave oven. The fat was then filtered and dissolved in hexane. This analysis was performed on a column (30 m x 0.25 mm i.d.) coated with a bonded stationary phase DB-17HT (50% phenyl-50% methylpolysiloxane; 0.15 microm film thickness) with hydrogen (2.1 mL min(-1)) as a carrier gas, programmed temperature was kept at 320 degrees C, and was then raised to 350 degrees C at a rate of 2.0 degrees C min(-1) and flame ionization detector. By using the triacylglycerols as chemical descriptors, pattern recognition techniques were applied to differentiate between montanera and cebo fattening diet of Iberian pig. Triolein, palmitoyl-stearyl-oleoyl glycerol and di-oleoyl-linoleoyl glycerol were found to be the most differentiating variables.