It is possible to create a probe against a target with high nt variation, such as an RNA virus, by using degenerated bases at variable positions but the degeneracy of the probe is dramatically increased by each wobbling base, thus decreasing the effective probe concentration. For instance, a sequence with two wobbling bases present in nine positions of variation would give a degeneracy of 512 unique sequence combinations, while a target with 14 variations including A, T, C or G would demand a set of 268 Â 10 6 unique probes (degeneracy 268 Â 10 6 ). Honoreé t al. successfully used 18-23 nt probes with a degeneracy of up to 512 in 3 M TMAC buffer (40) . In the more stringent PCR buffers, the usage of probes with a degeneracy greater than 10 is not often reported (41) . Degenerated primers have the property of being 'forgiving' (41) (42) (43) . This is because the amplimer from a previously successful primer is a target for the same pool of primers in the next round of amplification, leading to an accumulation of amplifiable targets. However, the situation for a probe is different. A degenerate probe will always face the same target variation. Therefore, universal bases like dInosine may be more useful than degenerated sites for probes, as long as the hybridization strength (represented by T m or -ÁG) is good enough. The introduction into a probe of a universal base like dInosine instead of a wobbling base reduces the complexity of the oligonucleotide mixture and increases the actual number of hybridizing oligonucleotides.