Environmental enrichment strategies are usually regarded as refinement. However, when the welfare of animals is enhanced through successful enrichment programmes, a reduction in the number of animals needed can be expected, because fewer animals might be lost during the course of experiments. Several examples of studies where enrichment can lead to reduction will be presented. They include the beneficial effects of nesting material for laboratory mice, the effects of husbandry procedures on controlling aggressive behaviour in male laboratory mice, and the effects of enrichment on variation in the results of experiments.