An unfortunate error arose in our previous paper ‘Electrofocusing and twodimensional electrophoresis of bovine caseins’ by P. Trieu-Cuot & J.-C. Gripon, Journal of Dairy Research (1981) 48 303–310. A paragraph describing the 2-dimensional electrophoresis technique in ‘Materials and Methods’ (p. 304) should read as follows:

The running gel was a linear gradient gel obtained with 2 starting solutions: (i) 28% acrylamide.0·7% bisacrylamide,4·9 M-urea,0·675 M-Tris-HClpH 8·8,0·1% SDS, 6·0 % sucrose, 0·04% TEMED, 0·012% ammonium persulphate; (ii) 16% acrylamide, 0·4% bisacrylamide, 4·9 M-urea, 0·675 M-Tris-HCl pH 8·8,0·1% SDS, 0·04% TEMED, 0·012% ammonium persulphate.