Reduction of the disulphide groups in wool keratin by various substituted phosphines has been studied. Tri(hydroxymethyl)phosphine and tri(diethylaminomethyl)phosphine effect considerable reduction but with these reagents side reactions also occur, probably due to the formation of formaldehyde, as they hydrolyse in aqueous solution. With tri-n-butylphosphine the reduction is apparently specific and nearly quantitative. Only a slight excess of this reductant is required.