The details of the construction of a cylindrical spark chamber made from 0.8 mm lead sheets clad with stainless steel foil and subtending a large solid angle are described. Its performance in the study of the reaction π++p→π++π0+p is discussed. In particular, the detection efficiency for this reaction, the kinematic resolution resulting from the analysis of the final state angles and the detection efficiency for low energy gamma rays are given. © 1968 The American Institute of Physics.