The relationship between in situ protein degradability and N solubility in three solvents was investigated in a range of ruminant feedstu †s with di †erent physical characteristics and crude protein (CP) content. In addition, relationships between N solubility in the three solvents and classical protein fractions (albumins, globulins, prolamins and glutelins) and also between protein fractions and soluble non-protein N or total true protein were examined. For all types of feedstu †s, a relatively high correlation (r \ 0É52È0É75) was found between dry matter (DM) degradation in sacco and protein solubility in the three solvents, but there was no close relationship between protein degradation in sacco and protein solubility in any of the three solvents used, or between CP content of feedstu †s and ruminal protein degradation, or between the estimates of ruminal protein degradability and the rate constant for protein disappearance from the rumen. However, when the feedstu †s were categorised into groups of the same type, there was a high correlation (r \ 0É64È0É91) between DM or ruminal protein degradation and solubility in the three solvents. A negative correlation (r \ [0É60 to [0É71) was found between CP content of feedstu †s and solubility in any of the three solvents used for all feedstu †s. There was no relationship between 1É5 or 3 h protein disappearance from the rumen and protein solubilities measured in the three solvents. The amount of N extracted by the three solvents for all feedstu †s was highly correlated between the solvents ie McDougallÏs bu †er vs 0É02 M NaOH (r \ 0É91), 0É02 M NaOH vs 0.15 M NaCl (r \ 0É79), and McDougallÏs bu †er vs 0É15 M NaCl (r \ 0É85). There was a signiÐcant correlation between the albumin fraction and N solubility in 0É02 M NaOH and a negative and signiÐcant correlation between the glutelin fraction and N solubility in McDougallÏs bu †er. Moreover, there was a signiÐcant correlation between the combined albumin and globulin fractions and N solubility in McDougallÏs bu †er and 0É02 M NaOH. The albumin, globulin, prolamin and glutelin fractions were all highly correlated with the CP content of feedstu †s and total true protein.