In purse seine fisheries, there may exist potentials for size selection because some of the fish in the catch are less than the legal size, and because different size groups are paid differently. Both potentials are present in the purse seine fishery for saithe along the Norwegian Coast, and at present the latter is of great interest in the mackerel fishery in the North Sea. We have developed a technology for size selection of fish in purse seine based on rigid sorting grids of polyester composite or aluminium mounted to the bunt. The size selection process takes place when the catch is concentrated in the bag along the side of the vessel. The grids give sharp size selection both for mackerel and saithe, and they have a substantial capacity for sorting out small fish.