Transplantation of olfactory ensheathing cells (OECs) into photochemically damaged rat spinal cord diminished astrocyte reactivity and parenchyma cavitation. The photochemical lesion performed at T12--L1 resulted in severe damage to the spinal cord, so that during the first 15 days postoperation all rats dragged their hindlimbs and did not respond to pinprick. The maximal area and volume of the cystic cavities were lower in transplanted than in non-transplanted rats, not significantly at the T12--L1 lesion site, but significantly at T9--T10 and L4--L6 cord levels. The density of astrocytes in the grey matter was similar at T12--L1 and L4--L6 in non-transplanted and trans- planted rats, but lower in the latter at T9--T10 level. However, in non-transplanted rats all astrocytes showed a hypertrophied appearance, with long and robust processes heavily GFAP-positive, and overexpression of proteoglycan inhibitor of neuritogenesis, whereas in transplanted rats only a few astrocytes showed hypertrophy and the majority had short, thin processes. These results indicate that OECs transplanted into damaged adult rat spinal cord exert a neuroprotective role by reducing astrocytic gliosis and cystic cavitation.