We report on the performance of a fine-grained 13-ton lead/scintillating-fiber calorimeter, in particular on its response to electrons, pions and multiparticles (reaction products from pions interacting in a target upstream of the detector). The detector signals were studied for particles in the energy range 5-150 GeV. The energy resolution was measured to be 12.9% √E for electrons, plus a constant term dependent on the angle θZ between the particle's direction and the fiber axis. This term, which is 1.2% for θz = 3°, is shown to be due to anomalous sampling in the early shower stage. It is greatly reduced when only electrons entering the detector in the lead are considered. A 1.7X0 thick preshower detector, installed 12 cm in front of the calorimeter, only affected the signal linearity for electrons at low energy. The effect on the energy resolution was negligible. Single pions were detected with an energy resolution of ∼ 30%/√E plus a constant term, which turned out to be mainly due to the effects of light attenuation in the fibers. Knowing the impact point of the particles, these effects could be efficiently removed for single pions. For jets (multiparticles), the effects of light attenuation are much less important, leading to considerably better on-line energy resolutions. The e π signal ratio was measured to range from 1.03 at 80 GeV to 1.10 at 5 GeV, for a detector with an effective radius of 49 cm. After correcting for the instrumental effects, we found the intrinsic e h value of this detector (with our particular choice of fibers and sampling fraction) to be 1.15±0.02. Detailed results are given on the detector performance (energy resolution, e π signal ratio, e/jet signal ratio) as a function of the lateral detector size and as a function of the jet multiplicity.