Patterns of early and late replication in the individual chromosomes of the Djungarian hamster (Phodopus sungorus) have been studied using the techniques of Giemsa staining suppression when bromodeoxyuridine is incorporated into the DNA.--Late replicating autosome regions correspond to G-band regions, early replication regions are less clearly demarcated but correspond to R-band regions plus some G-band zones. In part this reduction in sharpness of early replication bands may be due to the fact that nearly all metaphase G-bands contain R-band material since they are compounded from blocks of sub-G bands.--The long arm of the X chromosomes in the female differ in the start time of synthesis but are rarely separable at the close of S. There are no differences between the short arms. In the male, Y starts very late but finishes about the same time as the X which behaves like the early replicating X of the female.