Résumé : A study has been made of the K- meson absorptions at rest in emulsion nuclei of the type K- + nucleus → π- + charged particle + hypernucleus. The existence of the particle unstable resonant state of the Λ12C hypernucleus, decaying via Λ12C → 1H + Λ11B, has been firmly established. The excitation energy and natural width of this state are about 11 MeV and 0.4 MeV respectively. © 1972.