Abstract: In a process for mercerizing cellulosic cloth by treating the cloth with 3-10% caustic solution at the boil in a boilout stage, washing the cloth after treatment in the boilout stage and treating the washed cloth with 20-25% caustic in a mercerizer, an improvement comprises the steps of:(a) collecting overflow from the boilout stage, contaminated with additives used in weaving or knitting the cloth;(b) treating the contaminated overflow from the boilout stage by hyperfiltration to produce a recovered fraction of relatively pure caustic solution and a concentrate fraction containing additives used in weaving or knitting the cloth;(c) washing the cloth after treatment in the boilout stage with the recovered fraction of relatively pure caustic from step (b).