The replicative form (RF) DNA of chicken anaemia agent (CAA) was isolated and cloned into bacterial plasmids. After religation of the cloned CAA DNA and transfection into MDCC-MSB1 cells, the DNA could induce c.p.e. characteristic of that caused by CAA, and an antigen was produced which gave positive immunofluorescence when detected with an anti-CAA serum. Sanger sequencing of the 2298 bp genome revealed several open reading frames (ORFs); the major ORF encoded a polypeptide of 51.8K. In SDS-PAGE of CAA viral particles a 50K protein has been reported as the only detectable viral protein. The genomic region downstream of the major ORF had several predicted GC-rich inverted repeats, a poly(A) signal and four copies of an 18 bp repeat element. Database searches did not reveal any sequence with homology to the viral genomic DNA, nor to the amino acid sequence of any of the ORFs, apart from the N-terminal 40 amino acids of the major ORF which showed a limited similarity to the structure of protamines.