Interaction of the Columbia root-knot nematode, Meloidogyne chitwoodi, with Brassica spp. was studied in pot and in Petri dish experiments for 11 nematode isolates and three F-1 hybrids of cauliflower, broccoli and rapeseed. In the pot experiment, the host status of the different Brassica hybrids varied greatly (average of 4-45 egg-masses). The isolate-by-cultivar interaction effect was significant but depended only on three exceptions to the generally equal patterns for all isolates. In the Petri dish experiment, this large variation in aggressiveness was confirmed. Cauliflower, as a host for M. chitwoodi, is less favourable than rapeseed, and rapeseed is less favourable than broccoli. Several mechanisms are involved in the host-parasite interaction: limitation in penetration, in juvenile development, and in female-male ratio, each one acting with a high level of specificity to the isolates tested. No hypersensitive reaction was observed. In view of this quantitative resistance reaction, the species M. chitwoodi expresses an extremely large variability in terms of aggressiveness