The presence of siderophile-enriched material at the Cretaceous-Tertiary boundary suggests that the major extinctions of living species could result from cosmic catastrophes. The flnding of the same kind of material at the Permian-Triassic boundary would be important to conflrm the influence of cosmic phenomena on extinctions. The study of the Meishan section, in China, does not provide any support to this view. Iridium, the best tracer of cosmic material, has not been detected in any of the 18 samples collected around the boundary. A relation between the Permian-Triassic extinction and a cosmic collision therefore remains hypothetical.