Presumed piRNAs from Ae. aegypti are modified at their 3' ends. Control synthetic 23-mer RNA and purified 28-32 nt RNAs from Ae. aegypti were subjected to periodate oxidation and β-elimination reactions and run on a denaturing polyacrylamide gel. Synthetic 23-mer control RNA gained mobility, as expected for an RNA not modified at its 3' end while presumed piRNAs from Ae. aegypti failed to gain mobility, consistent with these RNAs being modified at their 3' ends.