In many sedentary nematode/plant combinations the nematode, once in the root, pierces the endodermis and induces feeding cells (giant cells) within the central cylinder. These cells develop extensive wall ingrowths adjacent to the vascular elements, suggesting that the bulk of solutes enters the giant cells from the apoplast. Physiological changes of the root system following infection, such as enhanced mineral/metabolite leakage and an increased uptake rate of ions assumed to be transported mainly via the apoplast, have been demonstrated. It has been suggested that the nematode maintains an apoplastic pathway for solute movement into, as well as out of the central cylinder. To trace whether there is such an apoplastic pathway between the cortex and the central cylinder of tomato roots (Lycopersicon esculentum Mill cv. Moneymaker) infected by Meloidogyne incognita (Kofoid & White), the movement of two fluorescent dyes into the central cylinder and their possible translocation to the giant cells was followed. Disodium, 4,4'-bis (sulfostyryl) biphenyl (Tinopal CBS), a blue fluorescent dye which binds strongly to cellulose, and the more mobile dye trisodium, 3-hydroxy-5,8,10-pyrene trisulphonate (PTS), a green fluorescent dye which does not bind to the cell walls, were applied to uninfected and infected root systems. The uptake of both dyes is restricted to the apoplast. The Tinopal CBS- and PTS-treated roots were rinsed in tap water for 1 h and for a few seconds, respectively. Handcut sections were viewed with a fluorescence microscope with suitable filters.