Plant parasitic nematodes are important plant pests which are difficult to identify and quantify. Serologically based techniques offer new ways to identify and quantify these parasites. Several factors need to be considered when developing an immunoassay for plant parasitic nematodes, including the application of the assay and the extraction procedure which together determine the likely organisms with which antibodies may cross-react. The four major factors: taxon specificity, nematode stage specificity, antibody specificity, and the level of management which is possible, need to be addressed interdependently and the best possible compromise made to develop a practical assay. Progress has been made in the immuno-diagnosis and quantification of potato cyst nematodes (Globodera spp) and root-knot nematodes (Meloidogyne spp) and these two groups of nematodes present different problems and therefore different challenges. The research reported here compares and contrasts work on these two groups of nematodes and highlights some of the important factors to be considered in the development of immunoassays for plant parasitic nematodes.