The vibrational spectra of the arabinonucleoside 9-beta-D-arabinofuranosyladenine, ara-A, are reported. Ara-A is of interest because of its antiviral activity. An accurate knowledge of the vibrational modes is a valuable help for the elucidation of drug-nucleotide and drug-enzyme interactions. The FTIR and FT-Raman spectra of ara-A were recorded from 4000 to 30 cm(-1). A hexadeuterated derivative (deuteration at C8, the amino and hydroxyl groups) was synthesized, and its spectra were also used for the vibrational analysis of ara-A, Theoretical frequencies as well as the potential energy distribution of the vibrational modes of ara-A were calculated using the ab initio HF/3-21G method, the semiempirical PM3 method, and two valence force fields. The results obtained are compared in order to show the accuracy and reliability of each method. The observed spectra and the vibrational frequencies of ara-A are assigned considering the potential energy distributions and the observed band shifts by deuteration. Scaled ab initio and PM3 frequencies are in a good agreement with the experimental data. The valence force field was found to reproduce them with enough accuracy when a large set of harmonic force constants is used. Previous normal coordinate analyses of the adenine and related molecules are compared with these results.