In STS-content mapping of a region, multiple optimal or near-optimal putative orders of markers exist. Determining which of the markers in this region can be placed reliably on the physical map of the chromosome and which markers lack sufficient evidence to be placed requires software that facilitates exploratory sensitivity analysis and interactive reassembly with different subsets of the imput data and that also assists the evaluation of any arbitrary (user-specified) marker order. We describe CONTIG EXPLORER, a package for interactive assembly of STS-content maps that provides the user with various ways of performing such analyses, thereby facilitating the design of laboratory experiments aimed at reducing ambiguity in STS order. We then compare the output of CONTIG EXPLORER with two other assembly programs, SEGMAP and CONTIGMAKER, for a region of chromosome 12p between 21 and 38 cM on the sex-averaged CEPH/Généthon linkage map.