Serology for parvovirus B19 has been hampered by limited availability of antigen which has often had to be isolated from viraemic blood donations. We have determined the sequence of the genome of one such isolate (Stu). It is 99% similar to the sequences of two other isolates (Wi and Au) except at the far 5'-end, where it is more similar to the terminus of another isolate (Ala/Alb). Recombinant nonstructural protein, NS, was constructed. Antibodies to NS, as well as to the capsid proteins, VP1/2, were detected in patients with B19 infection.