A dual-flow continuous-culture system was used to study the effects of protection method on protein degradation of soya-bean meal (SBM) by rumen bacteria. Treatments included solvent extraction (control), sodium hydroxide, ethanol, formaldehyde, expeller processing, propionic acid, extrusion and lignosulfonate. Diets contained approximately 17.0% crude protein, with 50% of the crude protein coming from the respective treated SBM and were fed to rumen bacteria in fermenters at a rate of 75 g dry matter day-1. Crude protein degradation of formaldehyde-treated, expeller processed, propionic acid-treated, extruded and lignosulfonate-treated SBM diets were lower (P < 0.05) than the control diet. Sodium hydroxide and ethanol treatments did not affect (P < 0.05) crude protein degradation. Total bacterial N output was lowest (P < 0.05) for SBM protected by formaldehyde, expeller processing and lignosulfonate treatments. Undegraded dietary N in the effluent was highest (P < 0.05) for SBM protected by formaldehyde, expeller processing, propionic acid and lignosulfonate treatments. Protection by formaldehyde, expeller processing, propionic acid and lignosulfonate treatments increased (P < 0.05) total amino-acid flow compared with the control. Formaldehyde and expeller processing treatments also increased (P < 0.05) essential amino-acid flow compared with the control. An in sacco study was also conducted which showed that treatment of SBM with formaldehyde, lignosulfonate, or expeller processing resulted in the greatest (P < 0.05) reduction in protein degradation.