Details of a reintroduction of Maculinea teleius (scarce large blue butterfly) and Maculinea nausithous (dusky large blue butterfly) into a nature reserve in the Netherlands are given. The introduced population of M. teleius expanded during the first three years. In contrast, the newly established population of M. nausithous declined in the year after the reintroduction but expanded later. After a considerable increase in numbers, this species can nowadays be seen in two subpopulations: one in and one outside the nature reserve. Although the results are quite positive with respect to the numbers of butterflies, some alarming features have also been found. Both species, but especially M. teleius, have a very low mean minimal lifetime, which makes them more susceptible to stochastic catastrophes. While the area populated by M. nausithous is still expanding, M. teleius can only be found on the meadow where it was released and has not dispersed at all. The possible consequences of reintroductions are discussed.