Stephen J.G. Hall School of Agriculture, De Montfort University, Caythorpe, Grantham, UK Valuation in the context of biodiversity is the process of determining the importance of consequences of economic activity that are not taken into account in market transactions (chapter 12 of Heywood and Watson, 1995). Valuation might in principle help with deciding the allocation of resources to conservation of Animal Genetic Resources (AnGR). There are two aspects to this issue; one seeks to place a valuation on AnGR so their priority for conservation can be compared with other ventures. The other seeks to establish the relative importances of different breeds as candidates for conservation. Current market signals worldwide are leading to loss of AnGR. Discussions on AnGR in Africa must bear in mind that introgression often comes not from the exotic (i.e. non-African) breeds such as the Holstein-Friesian that have so often been seen as a cause of loss of genetic variation. A local breed may receive genetic introgression from another breed of the region. Introgression from exotic breeds will however be important in pigs and poultry. Introgression can lead to breed replacement in that the local breed is 'graded up to' (acquires in an asymptotic manner the genotype of) the other breed; sometimes grading-up is incomplete and the result is a hybrid swarm resulting from matings among crossbred animals. In many parts of west central Africa, the indigenous humpless shorthorned cattle (the west African Shorthorn breed group: WASH) are being replaced in their traditional range (the humid forest and certain parts of the savanna) through crossbreeding with zebu genotypes (Jabbar et al., 1997; Blench, 1999). Although the WASH can tolerate trypanosomosis and presumably, like the Ndama (Mattioli et al., 1995) other local diseases, developments in husbandry and environmental changes are permitting the trypanosusceptible zebu genotypes, which the market prefers (Jabbar et al., 1997, 1999), to colonise these areas. As the grading-up proceeds, the WASH breeds will lose their distinctiveness and their trypanotolerance is reduced stepwise (Achukwi et al., 1997). Market prices favour the graded-up genotype and the economic value of this breed replacement, to the farmer, can in principle be calculated directly. But loss of the purity of the WASH genotype would deprive future generations of the option of using it. Use might be in crossbreeding schemes that exploit additive and heterotic effects sustainably, or as a source of genes conferring specific adaptations which are much easier to retrieve from the pure genotype than from a hybrid swarm.