The activities of the enzymes NTPDase (EC 3.6.1.5, apyrase, CD39) and 5'-nucleotidase (EC 3.1.3.5, CD73) were analyzed in platelets from rats submitted to demyelination by ethidium bromide (EB) and treated with interferon beta (IFN-beta). The following groups were studied: I - control (saline), II - (saline and IFN-beta), III - (EB) and IV - (EB and IFN-beta). After 7, 15 and 30 days, the animals (n=7) were sacrificed and the platelets were separated by the method of Lunkes et al. [Lunkes, G., Lunkes D., Morsch, V., Mazzanti, C., Morsch, A., Miron, V., Schetinger, M.R.C., 2004. NTPDase and 5'-nucleotidase in rats alloxan- induced diabetes. Diabetes Research and Clinical Practice 65, 1-6]. NTPDase activity for ATP and ADP substrates was significantly lower in groups II and III after seven days, when compared to control (p<0.001). At fifteen days, ATP hydrolysis was significantly lower in group III and IV and higher in group II (p<0.001), while there was an activation of ADP hydrolysis in group II (p<0.001), when compared with the control. 5'-nucleotidase activity was significantly higher in group IV (p<0.001) after seven days, and lower in the groups III and IV (p<0.001) after fifteen days in relation to the control. No significant differences were observed in NTPDase and 5'-nucleotidase activities after thirty days. In conclusion, our study demonstrated that the hydrolysis of adenine nucleotides is modified in platelets of rats demyelinated and treated with IFN-beta.