The extent of ruminal protein degradation of 13 roughages was determined in the rumen of cannulated lactating dairy cows, and was calculated at three different fractional outflow rates using the in situ polyester bag technique. Values ranged from 25,5% for Smuts finger grass hay to 79,5% for maize silage, when calculated at a fractional outflow rate of 0.08 / h. Extent of ruminal degradation was higher for silage, lucerne hay, ammoniated roughages and high-quality pastures than for low-quality roughages such as Smuts finger grass hay, teff hay and Eragrostis curvula hay.