The surfaces of plant and animal parasitic nematodes share certain lipids, which seem to be important in the infection process. The surfaces of 2 parasitic nematodes, Meloidogyne incognita and Haemonchus contortus, were activated by different pH buffers to allow the insertion of different fluorescent probes. The lipid analogue PKH26 and the surface charge indicator, cationized ferritin, were used as probes with these nematodes but labelled only the retaining 2nd-stage moulted cuticle of H. contortus 3rd-stage larvae (L3). Shedding of the second moult of H. contortus L3 was also visualized with PKH26 and cationized ferritin. The fluorescent anionic lipid probe 5-N-(octadecanoyl)-aminofluorescein (AF18) was inserted into the epicuticle layer of M. incognita 2nd-stage juveniles (J2) and H. contortus L3, and also of the second moult of H. contortus L3. Incubation with tomato root diffusate caused modifications of the M. incognita surface allowing the insertion of AF18. Fluorescence with AF18 was significantly decreased after treating M. incognita J2 with amiloride, a potent blocker of hydrogen and sodium (H+/Na+) antiporter. No surface fluidity was observed in M. incognita J2 and H. contortus L3 pre-treated with alkaline buffer when the lipid analogue AF18 was used in fluorescence recovery after photobleaching experiments. The significance of these findings to host infection processes is discussed.