Sensitive assays capable of detecting proteinases in single females of the phytoparasite Globodera pallida have been developed and used to define the proteinase activity of young adult females. Digestion of the large subunit of the plant protein Rubisco established a pH optimum for the proteinase activity at pH 5·7. The activity was inhibited by the cysteine proteinase inhibitors p-chloromercuribenzoic acid (PMBA) and p-chloromercurisulphonic acid (PMSA) and stimulated by both cysteine and dithiothreitol (DTT). It was moderately reduced by L-trans-epoxysuccinyl-leucylamido-(4- guanidino) butane (E64) but not by specific inhibitors of serine, aspartate or metallo-proteinases. The activity separated into 3 bands on a non-denaturing gel but only I proteinase of 62 kDa was recovered following a combination of anion-exchange chromatography and affinity chromatography using PMBA. The effect of inhibitors was similar to that reported previously for some of the cysteine proteinase activity recovered from Caenorhabditis elegans but is apparently not that for which the corresponding gene has been cloned in this nematode and Haemonchus contortus. The proteinase may have a major role in digestion of dietary protein and so offers an exciting target for future control of this important plant-parasitic nematode.