Polyommatus coridon (Poda, 1761) is represented by endemic subspecies on the Mediterranean islands of Corsica (nufrellensis Schurian, 1977) and Sardinia (gennargenti Leigheb, 1987). The latter taxon is considered a separate species by some authors, but evidence for reproductive isolation is lacking. In order to check for isolating mechanisms we carried out hybridisation experiments. Source material for these experiments were ♀♀ which had been caught for oviposition in 2007. We achieved synchronous hatching and development of larvae by keeping them under long-day conditions and high temperatures. With the help of the “semi- artificial method” we obtained 6 matings between ♀♀ of P. c. nufrellensis and ♂♂ of P. c. gennargenti, whereas the reciprocal copulation was only achieved once. 4 of the ♀♀ laid 155 eggs altogether, of which 79% proved fertile. Resulting caterpillars were reared under the above-mentioned laboratory conditions using Hippocrepis comosa, and from mid-November, after about 6 weeks, developed into adults of the F1 generation (18 ♂♂, 22 ♀♀, 24 pupae died, 1 adult crippled). Almost all hybrids appear intermediate between the parents. We did not find evidence for reproductive isolation barriers because mortality rates of the hybrid breedings did not differ considerably from pure breedings.