The mouse serotonin 1F (5-HT1F) receptor is encoded by at least three transcripts in mouse brain. These transcripts are expressed predominantly in cortex and hippocampus. Similar transcripts are seen in Northern analysis of rat brain mRNA. 5' RACE showed a predominant transcription start site around 350 bp upstream of the translational start present in mouse cDNA. Our results suggest that the heterogeneity seen in transcript size is due to differences in the 3' untranslated region, which could play a critical role in mRNA targeting and localization. The mouse 5-HT1F genomic clone shows the coding region to be intronless and an intron splice junction is seen in the 5' untranslated region which is conserved in both rat and mouse.