Splicing is one of the major post-transcriptional modifications a eukaryotic mRNA precursor (pre-mRNA) has to undergo to yield the mature mRNA. During pre-mRNA splicing the non-coding sequences (introns) of the precursor are removed and coding sequences (exons) are joined. This process takes place within a complex called a spliceosome and requires the presence of a number of splicing factors such as small nuclear ribonucleoprotein particles (snRNPs). Oligonucleotides containing sequences complementary (antisense) to unique sequences within the pre-mRNA can be used to modify splicing and, thus, gene expression. Likewise, snRNPs provide another important target for using antisense oligonucleotides as investigative tools to further study the mechanism of splicing. This article reviews the available literature on the use of antisense oligonucleotides targeted against pre-mRNA and those targeted against small nuclear ribonucleoprotein particles (snRNPs) within the spliceosomal complex.