The extent of proteolysis in two sets of Stilton (England), Gorgonzola (Italy), Danablu (Denmark) and Irish farmhouse varieties (Cashel and Chetwynd) was studied. High levels of pH 4.6-soluble N and similar amino acid profiles were found for all cheeses but the concentration of most amino acids was substantially higher in Gorgonzola than in the other varieties. Glutamic acid, leucine, lysine and valine were the principal amino acids and represented about 45% of the total. Urea-polyacrylamide gel electrophoresis showed extensive degradation of both alpha(sl)- and beta-caseins. Reverse-phase HPLC profiles of the pH 4.6-soluble extracts from Stilton and Danablu were similar, but the profile for Gorgonzola was quite different and contained considerably higher concentrations of small peptides and free amino acids. The concentrations of peptides with intermediate elution times were substantially higher in Cashel blue than in the other cheeses. The profile of Chetwynd was qualitatively similar to that of Stilton and Danablu, but showed quantitative differences; corresponding peaks were smaller in Chetwynd. The sub-fraction soluble in ethanol (70 ml / 100 ml) contained almost all peptides detected in the pH 4.6-soluble fraction. The reverse-phase HPLC chromatograms of the ethanol-insoluble fractions were quite different from those of the ethanol-soluble fractions; the chromatograms of all cheeses contained large peaks eluting between 28 and 40 min.