High-velocity (~2 to ~5 km/sec) impacts into meteorites (Gibeon, El Sampal, and Arispe), steel, and iron targets were made at the NASA-Ames Vertical Gun Facility. The experiments clearly revealed the brittle behavior of meteorites at very low temperatures (<200¿K) as indicated by spallation of the crater rim and the development of deeply penetrating fractures in the meteorite sample. Although failure also occurred at higher temperatuares (290¿K), it was restricted to near-surface spalls. High-velocity (~5 km/sec) impacts resulted in a net mass loss regardless of the brittle-ductile behavior of the target or projectile, whereas low-velocity (~2 km/sec) impacts resulted in a net mass gain for ductile projectiles into brittle and ductile targets. Consequently, even if iron meteorites (octahedrites) were originally the core of a layered parent body, they might be subsequently destroyed in a brittle manner. Such results are consistent with the hypothesis by Matsui and Mizutani (1977) that the brittle behavior of iron-like planetesimals in the low-temperature asteroid zone prevents growth into full-size planets.