A dot-blot hybridization assay was developed to detect B19 DNA using strand-specific RNA probes labelled with digoxigenin. The sensitivity of the assays was evaluated either using 'plus' and 'minus' sense RNA probes in two different hybridization assays, or in two successive reactions of the same assay. The hybridized probes were revealed immunoenzymatically using anti-digoxigenin Fab fragments conjugated with alkaline phosphatase. The enzyme was visualized by colorimetric reaction. Since 'minus' sense RNA probe gave the best results in the dot-blot procedures, we increased the sensitivity of the hybridization assay visualizing the 'minus' sense digoxigenin-labelled RNA probe by chemiluminescent reaction. In these experimental conditions up to 20 fg of target B19 DNA could be visualized. In the search for B19 DNA, 4656 serum samples were analyzed by chemiluminescent reaction of 'minus' sense digoxigenin-labelled RNA probe and for comparison with the digoxigenin-labelled DNA probe. Positive results were confirmed by Southern blotting. Out of 4656 serum samples analyzed, 4648 gave negative results, 1 resulted positive to all the hybridization assays, 6 only using RNA probe and 1 only by DNA probe.