DNA complementary to the tenth largest (S10) of the 12 genome segments of rice dwarf virus (RDV) was cloned and its sequence was determined. This genome segment is 1319 nucleotides in length and has a single long open reading frame extending for 1059 nucleotides from the first AUG triplet (residues 27 to 29). The predicted translation product comprises 352 amino acids and has a mol. wt. of 39094. RDV transcripts synthesized in vitro have the same polarity as the plus strand of the genome. Terminal sequences were (+) 5' GGUA---UGAU 3' and (-) 3' CCAU---ACUA 5' which are similar to those of wound tumour virus RNA.