A cocktail of 10 oligonucleotides selected at intervals along the length of the genome of human parvovirus B19 was labelled enzymically with digoxigenin and chemically with either digoxigenin (DIG) or dinitrophenyl (DNP). Chemical labelling was easier and more practical for the production of large quantities of probe. Pools labelled with either digoxigenin or DNP could detect 10 fg of B19 DNA in a dot blot reaction using an alkaline phosphatase antibody conjugate and colorimetric detection. Formalin fixed tissue from 11 consecutive cases of fetal hydrops were examined by in situ hybridisation (ISH). Both probe cocktails detected human parvovirus B19 DNA in 3 cases, with positive cells in all tissues examined and with equal sensitivity. The DNP pool is significantly cheaper and simpler to produce and could provide an inexpensive reagent suitable for diagnostic detection of viral nucleic acid in histopathological material.