The protein degradability of 13 South African ruminant feed protein sources were determined by the artificial fibre bag technique. Three sheep fed ad lib. on a basal diet of lucerne hay were used. Estimates obtained by two methods of calculation were not in good agreement for all the feeds studied. Assuming an arbitrary rate constant for passage of undegraded protein from the rumen of 0,05, the effective percentage nitrogen degradation for the various feedstuffs as calculated by the two methods was found to be as follows: Sunflower oilcake 85,83; groundnut oilcake 93,93; cottonseed oilcake 59,61; lupin 89,89;soyabean 92,92; maize 74,64; maize silage 88,84; lucerne hay 79,72; Eragrostis curvula hay 30,27; maize gluten feed 89,87; maize gluten meal 24,25; dried brewers grains (sorghum) 49,38; fishmeal 36,42. Protein solubility in NaOH gave no reliable indication of the rapidly-soluble protein fraction as determined by the artificial fibre bag technique.