Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) have been used to identify a new Ti3+ center in KTiOPO4 crystals containing lead impurities. Many of the K+ vacancies in this set of KTP crystals are compensated nonlocally by Pb2+ ions substituting for K+ ions. During exposure to ionizing radiation (either 60 kV x rays or 355 nm photons from a tripled Nd:YAG laser), “free” electrons are trapped on Ti4+ ions near isolated Pb2+ ions, thus forming the perturbed Ti3+ ions observed with EPR and ENDOR. Four distinct Pb-related Ti3+ centers are formed by a 77 K irradiation, but only one remains after a 5 min anneal at 180 K. This latter defect, labeled the [Ti3+–Pb2+]A center, is thermally unstable above 250 K. Angular dependence data were used to determine the g matrix, one 207Pb hyperfine matrix, and two 31P hyperfine matrices for the [Ti3+–Pb2+]A center. More generally, we note that oxygen-vacancy-associated Ti3+ centers could not be formed in these Pb-containing KTP crystals. Re- placing oxygen-vacancy-associated Ti3+ centers with the less stable [Ti3+–Pb2+] centers is expected to increase the gray-track resistance of KTP crystals used to generate the second harmonic of high power, near-infrared lasers. © 2000 American Institute of Physics.