crystallization of dye molecules in fibers is a controversial subject and is of great theoretical and industrial interest. high light-fastness and wash-fastness of some dyes and change of shade after soaping in vat dyeings of cellulose was assumed to be due to crystallization of dyes. previously, the authors reported electron diffraction (ed) patterns providing unambiguous evidence of the presence of dye crystallites in dyed cellulose fibers. since seeing is believing and morphological details of such crystals can be studied directly by visual observation, the authors concentrated their efforts on obtaining electron micrographs of these single dye crystals inside the fiber. in the present study, the layer expansion technique was adopted to separate lamellas containing macrofibrils so that the single dye crystals, if grown sandwiched between the lamellas could be seen in the transverse section of the fibers furthermore, the fibrillation technique was used to investigate the possibility that the single dye crystals might grow on the surface of a secondary cell wall and macrofibrils. in experiments, cotton fibers dyed with both ce- and pd-metallized azo dyes respectively were embedded flat in polymethacrylate following the layer expansion technique. electron micrographs of several samples are presented and evaluated. 12 refs