The aim of this experimental study was to investigate the possible role of nitric oxide (NO) levels and activity of adenosine deaminase (ADA) in the pathogenesis of methotrexate (MTX)-induced neurotoxicity, to demonstrate the effect of caffeic acid phenethyl ester (CAPE), the potent antioxidant, in decreasing the toxicity. A total of 19 adult male rats were divided into three experimental groups, as follows: group I, control group; group II, MTX-treatcd group; group III, MTX+CAPE-treated group. In the second day of experiment, MTX was administered intraperitoneally (i.p.) with a single dose of 20 mg/kg to group II and group III. CAPE was administered i.p. with a dose of 10 mu mol/kg once daily for 7 days to group III. Histopathological findings of the inflammatory reaction were observed in spinal cord of MTX administered rats, compared with control rats. All parameters of: inflammatory reaction were significantly decreased in MTX plus CAPE administered rats, compared with MTX administered rats. The injection of MTX caused significant increase in the activity of ADA and in levels NO levels in spinal cord of rats (p = 0.007 and p = 0.0001, respectively). Co-treatment with CAPE caused a significant decrease in activity of ADA and the levels of NO in spinal cord (p = 0.024 and p=0.0001, respectively). Study indicate that NO and ADA may play ail important role in the pathogenesis of MTX-induced oxidative spinal cord damage. CAPE may have protective aspects in this process by antioxidant and anti-inflammatory effect and it will become a promising drug in the prevention Of undesired side effect of MTX. (C) 2005 Elsevier Ireland Ltd. All rights reserved.