We present here the first detailed replication banding study of a marsupial species using the BrdU-replication technique. A comparison of the structural and replication bands of the chromosomes of Sminthopsis crassicaudata clearly demonstrates that the replication behavior is the same as that described for the chromosomes of eutherians. The early replicating segments correspond to R-bands, whereas the late-replicating regions tend to be situated within Q- and C-bands. Use of this technique clearly reveals an early and late replicating X chromosome. The very small Y chromosome can be subdivided into two replication segments, but no replication homologies can be demonstrated between the X and Y chromosomes of S. crassicaudata.