Multi-generation exposure of organisms to toxicants may lead to adaptations increasing their resistance to a chemical. However, the increased tolerance may have a negative effect on fitness in uncontaminated environments due to increased maintenance costs in adapted individuals. Herein we present results of a multi-generation experiment on the flour beetle, Tribolium confusum, showing that animals bred for ca. 10-13 generations in copper-contaminated medium had higher maintenance costs then their counterparts originating from uncontaminated medium. The results show that significant changes in energy budgets may occur even after relatively short selection in small laboratory cultures.