U12-type introns are found in most high eukaryotic organisms. Several data sets containing genes with this type of introns have been published. Three genes with U12 introns were followed in 13 different species. Some paralogous genes were also analysed. Conservation of introns in several species and in one gene family as well as possible intron loss are reported in the present study. Conservation only was found within vertebrates, and not in the same species for all the introns. Some differences from the consensus sequences of the donor and the branch sites are shown, suggesting that these sites could be less constrained than it is thought. It will be seen when more U12 introns are analysed.