The invention provides pharmaceutical compositions comprising short single strandedoligonucleotides, of length of between 8 and 26 nucleobases which are complementaryto human microRNAs selected from the group consisting of miR19b, miR21, miR122a,miR155 and miR375. The short oligonucleotides are particularly effective atalleviating miRNA repression in vivo. It is found that the incorporation of highaffinity nucleotide analogues into the oligonucleotides results in highlyeffective anti-microRNA molecules which appear to function via the formation ofalmost irreversible duplexes with the miRNA target, rather than RNA cleavage basedmechanisms, such as mechanisms associated with RNaseH or RISC.
