This publication contains the proceedings of a seminar held in Brussels on November 8-9, 1988. The title of the seminar was "Reducing the costs of disease by improving resistance through genetics." The seminar was held as an activity of the Community Programme for the Coordination of Agricultural Research, 1984-1988. Costs of disease depend on losses caused by morbidity, mortality and production decreases and on the costs of preventive measures including vaccination and medication. Production losses often contribute a major portion to the total costs. To reduce costs of disease preventive measures like vaccination, preventive medication and hygienic procedures are applied. Genetic resistance is an attractive preventive measure because of its consistent nature in the next generations, because it precludes veterinary services and because there are no side-effects. Constraints are the long term investment, relatively slow progress per generation (in combination with production traits) and the considerable lack of knowledge about inheritance of resistance mechanisms in farm animals.