The basic theory of linear elastic fracture mechanics was applied to the fracture of pods from six genetic lines of oilseed rape ( Brassica napus). An experiment was designed to allow the energetics of the fracture process to be accurately determined. The work of fracture, toughness and fracture toughness of five experimental varieties and one common commercial variety (Apex) were measured. The values for the toughness (0.006-0.271 kJ m(-2)) and fracture toughness (0.026-0.233 MN m(-3/2)) obtained from each line were distinct from each other but broadly similar to those of other brittle materials. The toughness and fracture toughness of Apex were approximately midway between the lowest and highest values measured. This result indicates that there is scope for improving the fracture resistance of oilseed rape crops so as to reduce seed loss before and during harvest. The approach described would be useful in selecting fracture-resistant genetic lines to help to develop such crops.