Nuclei and hypotonically leached extracts of nuclei prepared from tomato golden mosaic virus (TGMV)-infected Nicotiana benthamiana leaves have been used in in vitro DNA and RNA polymerisation reactions. The synthesis of virus-specific DNA was resistant to aphidicolin, sensitive to N-ethylmaleimide and dideoxy TTP, and stimulated by KCl and ATP. Variably virion (+) and complementary (-) strand DNA of both the A and B genomic components were synthesised. Virus-specific RNA was synthesised in reactions which were initiated prior to nuclei isolation and leaching. From inhibitor studies and salt requirements RNA synthesis appeared to be catalysed by a DNA-dependent RNA polynerase type II enzyme. Both components of the TGMV genome were transcribed in a bidirectional fashion with a prevalence in some experiments of transcripts derived from DNA component A.