Previously, Honore´et al. introduced up to three dInosines in radioactively labelled short oligonucleotide probes, 18-23 nt, in dot-blot hybridization, using a buffer containing 3 M TMAC (40) . The aim was to reduce the degeneracy in probes used for screening cDNA libraries. They found that dInosines had a slightly destabilizing effect on hybridization, especially when hybridizing against A, G and T, but that this could be minimized by reducing the hybridization temperature. However, the behavior of dInosine in long probes in 3 M TMAC has, to our knowledge, not previously been systematically explored. The 3 M TMAC is known to increase the binding contribution of the A:T base pairs, resulting in a similar contribution to T m to that from the G:C base pairs. The high ionic strength makes this an environment of relatively low hybridization stringency. The general trend shown in our study (e.g. Figure 2A and B), that dInosine in the probe decreases hybridization in 3 M TMAC, indicates that TMAC did not enhance the binding strength of dInosine base pairs as much as that of A:T base pairs; cf (8) . In a segment with dInosines at every third base, such as in the Ino18 probe, every matching nt neighbors a dInosine, i.e. it will not bind as strongly as a probe containing neighboring matches. Clearly, dInosine matches cause less destabilization than mismatches, and allow hybridization of probe/ target combinations with many short matching segments, like the InflA probe / 21-pm target combination. It is reasonable to assume that when a probe fails to hybridize due to a high number of mismatches in the target, dInosines at these positions will restore hybridization, since dInosine appears to bridge adjacent matching stretches, increasing their ability to nucleate.