A simplified R banding technic is described which provides excellent delineation of major regions, easy identification of all chromosomes, and an accurate comparison of homologue lengths. The technic is simple, requiring only an initial incubation in buffer at 85 degrees C followed by acridine orange staining. The best presentation of the R banded chromosomes was obtained by printing in black and white from color transparency film. Variations in the length of the short arms of the acrocentric chromosomes are clearly and consistently defined. Satellites are not demarcated and appear as part of the short arm. Consistent banding was obtained, and the technic is suitable for use in routine clinical cytogenetic work.