The DNA of three previously cloned interband regions (85D9/D10, 86B4/B6, and 61C7/C8) of Drosophila melanogaster polytene chromosomes has been tested for the presence of matrix association regions (MAR), using the in vitro matrix-binding assay of Cockerill and Garrard. MARs were found in all three interband regions under study. These results are discussed in frames of a model postulating that interband regions of polytene chromosomes correspond to the chromosomal DNA loop borders, which can be identified in interphase nuclei using biochemical approaches.