Deoxyribonucleoside kinases catalyze the rate limiting step during the salvage of deoxyribonucleosides and convert them into the corresponding monophosphate compounds. We have identified and characterized a unique multisubstrate deoxyribonucleoside kinase from plants. The phylogenetic relationship and biochemical properties suggest that this deoxyribonucleoside kinase represents a living fossil resembling the progenitor of the modern animal deoxycytidine, deoxyguanosine and thymidine 2 kinases. The broad substrate specificity makes this enzyme an interesting candidate to be evaluated as a suicide gene in anti-cancer therapy.