alpha-L-Rhamnosidase from Aspergillus terreus was covalently immobilized on the following ferromagnetic supports: polyethylene terephthalate (Dacron-hydrazide), polysiloxane/polyvinyl alcohol (POS/PVA), and chitosan. The powdered supports were magnetized by thermal coprecipitation method using ferric and ferrous chlorides, and the immobilization was carried out via glutaraldehyde. The activity of the Dacron-hydrazide (0.53 nkat/mu g of protein) and POS/PVA (0.59 nkat/mu g of protein) immobilized enzyme was significantly higher than that found for the chitosan derivative (0.06 nkat/mu g of protein). The activity-pH and activity-temperature profiles for all immobilized enzymes did not show difference compared to the free enzyme, except the chitosan derivative that presented higher maximum temperature at 65 degrees C. The Dacron-hydrazide derivative thermal stability showed a similar behavior of the free enzyme in the temperature range of 40-70 degrees C. The POS/PVA and chitosan derivatives were stable up to 60 degrees C, but were completely inactivated at 70 degrees C. The activity of the preparations did not appreciably decrease after ten successive reuses. Apparent K-m of alpha-L-rhamnosidase immobilized on magnetized Dacron-hydrazide (1.05 +/- 0.22 mM), POS/PVA (0.57 +/- 0.09 mM), and chitosan (1.78 +/- 0.24 mM) were higher than that estimated for the soluble enzyme (0.30 +/- 0.03 mM). The Dacron-hydrazide enzyme derivative showed better performance than the free enzyme to hydrolyze 0.3% narigin (91% and 73% after 1 h, respectively) and synthesize rhamnosides (0.116 and 0.014 mg narirutin after 1 h, respectively).