Parvovirus B19 DNA was detected in serum samples from 10 out of 42 patients with chronic anaemia, the majority of whom suffered from aplastic anaemia, haemolytic anaemia, pure red cell anaemia or myelodysplastic syndrome. Nested PCR methods with sensitivities of 0.005-0.05 fg DNA were developed. In nine patients, B19 DNA could only be detected by nested PCR. Conventional PCR with a sensitivity of 50 fg B19 DNA could only detect B19 DNA in one patient. In the majority of B19-DNA-positive patients, the DNA concentration was estimated at 0.005-0.05 fg per 5 microliters serum.