The selective and sequential extraction of the fractions of Al, Fe and Si (potassium chloride, sodium pyrophosphate, ammonium acid oxalate, dithionite-citrate-bicarbonate and sodium hydroxide) of a Andisol of the East of Antioquia was studied for genetic purposes, it allowed the separation of allophane and non-allophane horizons. In the A and 2B/A horizons, the colloidal fraction was dominated by organometallic complexes, whereas in the 3C/A and 4Bs horizons the aluminosilicates and the non-crystalline oxides and hydroxides predominated. This method also managed to differentiate within the horizon A, at least, two sub-horizons not visualized in the field. The low Ald, Fed and Sid and Aln and Fen contents reported may be due to the previous extractions made in the soil with sodium pyrophosphate and ammonium acid oxalate, in which the highest proportion of Al, Fe and Si was released, and to the low amounts of crystalline inorganic colloids present in the Andisols.