Different peptaibols were observed in both fresh and frozen marine sediments collected from a marine area devoted to bivalve culture (Fier d'Ars, Atlantic coast, France). The identification of the peptaibols was based on a three-step mass-spectrometric analysis: observation of doubly charged ions with a characteristic isotopic profile, cleavage and observation of C- and N-terminal fragments, and partial sequencing of the N-terminal segments. The MS characteristics indicated numerous similarities between the peptaibols detected and those produced by different strains of Trichoderma species isolated from fresh sediments. Peptaibols were also detected in mussel samples collected at the same site. This constitutes the first observation of contamination of the marine human-food chain by fungal metabolites. Since peptaibols were readily observed both in fresh sediments and in samples kept frozen for several years, these compounds can be considered as stable markers of the development of Trichoderma in the marine environment.