Résumé : From about 30 000 stopped K- mesons in the Ecole Polytechnique bubble chamber filled with CF3Br, a search has been made for long-range π- mesons due to the reaction K- + Br → → ΛBr + π-, in an attempt to determine a lower limit of the Λ binding energy in ΛBr. No event compatible with this reaction has been found. Results from measurements of the total π- and π+ energy spectra have been used to investigate the production and trapping of Λ hyperons in K- captures on complex nuclei. From the frequency of Λ production associated with the emission of π- mesons with kinetic energy > 110 MeV, the fraction of directly produced Λ hyperons being trapped in the production nuclei was estimated as 0.29-0.07+0.15. For Λ hyperons due to Σ conversion a lower limit for the same quantity is 0.28 ± 0.05. © 1966 North-Holland Publishing Co., Amsterdam.