The temperature dependence of the intensity of the EPR signal is measu
red in the high-temperature superconductor YBa2Cu3O6.85 and in the non
superconducting compound YBa2Cu3O6.25. The copper-oxygen cluster model
with spin S=2 best describes the results obtained in a sample with ap
r oxygen index of 6.25. The interpretation of the experimental results
for a sample with an oxygen index of 6.85, on the other hand, require
s the additional assumption that the cluster S=2 also has a 200-fold d
egenerate level at a distance similar to 110 K. (C) 1997 Institute of
physics.