We investigated the dynamic properties of the piNG-body, a large perinuclear granule that was discovered previously in spermatocytes of Drosophila. The piNG-body contains ribonucleoprotein complexes involved in piRNA silencing of genome repeats, including transposons in premeiotic spermatocytes, using short piRNAs. Confocal microscopy of fixed and native preparations has demonstrated that piNG-body is a mobile structure that does not occupy a stationary position near nuclear surface relative to chromosomal territories. FRAP analysis reveals a high exchange rate of RNA helicase Vasa in the piNG-body and small perinuclear granules with the cytosol Vasa pool. The disruption of the microtubule assembly of the cytoskeleton does not affect the stability of the piNG-body and small granules. We suppose that the combination of piNG-body mobility and permanent molecular exchange of Vasa protein provides an efficient scan of the total volume of cytoplasm in primary spermatocytes and timely recognition and destruction of unwanted transcripts of the repetitive elements of genome.