The genome of infectious bursal disease virus (IBDV) strain 002-73 was found to consist of two segments of double-stranded (ds) RNA which were 3400 bp (MW 2.06 X 10(6)) and 2900 bp (MW 1.76 X 10(6)) long, respectively. The ds IBDV RNA could be translated, in vitro, only after extensive denaturation. The small RNA segment was found to code for a single polypeptide of MW 90K, while the large RNA segment coded for three major polypeptides of MW 52K, 32K, and 28K, and two minor polypeptides of MW 41K and 16K. The large RNA segment could encode proteins of MW 125K while the MW of the translated products was 169K suggesting that a precursor-product relationship exists between some of the translation products. A method is described for the synthesis of ds cDNA from large ds RNA molecules. Analyses of recombinant colonies showed that inserts covering the entire IBDV genome had been cloned.