The absorption of C.I. Direct Red 81 and C.I. Direct Green 26 by cotton yarn subjected to mercerisation, drying and steaming treatments has been studied. Absorption isotherms suggest the formation of mono-layers of the red dye, and accessible surface areas have been calculated. The progress of acid hydrolysis of the cotton samples has been followed by measurements of D.P., regain and red dye sorption. The regains of hydrolysis residues suggest that during steaming a permanent fusion of fibrils had occurred. The results are interpreted in terms of a crystalline fibril model of the cotton fibre.