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The electron paramagnetic resonance spectra of Mn^{2+} and Cu^{2+} in Cs_{2}C_{2}O_{4}·H_{2}O single crystals are studied at ~9.45 GHz and 290 K. The spectra at 77 K show no appreciable change. The ions appear to enter the lattice at interstitial sites. The spin-Hamiltonian parameters are evaluated at 290 K.