Five short interspersed repetitive elements (SINEs) were found fortuitously in the introns of a steroid hormone receptor AaHR3-2 gene of the yellow fever mosquito, Aedes aegypti, constituting a novel family of tRNA-related SINEs named Feilai. In addition, nine other Feilai elements were found in currently available sequences in Ae. aegypti, six of which were also near genes. Approximately 5.9 x 10(4) copies of Feilai were present in Ae. aegypti, equivalent to 2% of the entire genome. An additional 35 Feilai elements were isolated from a genomic library. Of the total 49 Feilai elements, 20 were full-length. Sequence comparisons and phylogenetic analyses of the full-length elements strongly suggest that there are at least two subfamilies within the Feilai family. There is a high degree of conservation within the two subfamilies. However, sequence divergence between the subfamilies, along with the presence of highly degenerate Feilai elements, suggests that Feilai is likely a diverse family of SINEs that has existed in Ae. aegypti for a long time. Many Feilai elements were closely associated with other transposons, especially with fragments of non-LTR retrotransposons and miniature inverted-repeat transposable elements. The 500-bp sequences immediately flanking a Feilai element were highly A + T-rich, which is consistent with the fact that no Feilai has been found in the coding regions of genes. It is likely that the highly reiterated and interspersed Feilai elements are partially responsible for the pattern of short-period interspersion of the Ae. aegypti genome. The evolutionary relationship between Feilai and the Ae. aegypti genome is likely complex.