Treatment with trivalent cations: Fe and Al in the form of alums (2-40 g of metal/1 kg of feed) as a means of reducing degradation of field bean (FB) and rape seed (RS) protein in the rumen was studied using solubility tests and in sacco degradation as response criteria. The chemical treatments were also combined with autoclaving at 121°C for 10–30 min. and wet heating at 120° C for 20 and 30 min. The results were compared to the effects of formaldehyde. Iron alum was as effective as formaldehyde in reducing protein solubility of FB (P > 0.05) and more active than aluminium alum (P < 0.01). FB was more responsive to Fe than RS and reacted to increasing Fe concentrations up to 40 g/kg. In the range of 20-40 g Fe/kg, FB protein degradation was reduced by 34 to 51 units, respectively, that of RS by 26 to 31 units. Autoclaving in combination with Fe action was particularly effective in reducing ruminal degradability of FB (P < 0.001). The amount of undegraded protein from treated samples was 3–5 times higher than that in the non-autoclaved water-treated samples. The effect of autoclaving was much less pronounced on RS (P < 0.05), as was wet heating at atmospheric pressure (P > 0.05).