The borate G-banding technique produced excellent longitudinal bands similar to trypsin G-bands on chicken chromosomes prepared from embryo material. Aged chromosome preparations on slides were pretreated in borate buffer (pH 9.2) for 10 to 30 s at 37 C, then stained in Giemsa solution. This simple G-banding procedure gave high-resolution chromosome banding and permitted the visualization of silver grains that localized cloned gene sequences or cloned DNA fragments to specific regions by in situ hybridization.