The nucleotide sequence of the nucleocapsid (N) protein gene of Berne virus (BEV; proposed family Toroviridae) was determined from two independent clones of a cDNA library. From the deduced amino acid sequence a basic protein of 18.3K was predicted. In vitro transcription and translation, followed by immunoprecipitation, were used to identify the gene. The identification was confirmed by metabolic labelling, using the knowledge that cysteine residues are absent from the amino acid sequence of the N protein. Smaller N-related polypeptides encountered in BEV-infected cell lysates were shown to be probable products of aberrant translation, due to initiation on AUG codons further downstream in the N protein gene.