Abstract A high-resolution radiation hybrid map of human chromosome 18 has been developed by testing DNA samples of 92 radiation hybrids (RH) from a previously characterized chromosome 18-specific RH panel. Half of the 159 STS markers were tested on RH DNA amplified by primer extension preamplification. This map includes 20 genes and 95 polymorphic markers, most of which have heterozygosity frequencies greater than 65% and, therefore, allow integration with genetic maps. The framework map consists of 137 markers ordered with odds of 1000:1 or better and spaced on average 580 kb apart. A YAC contig map of 18p was generated independently by STS content mapping of YACs using the same primers as for RH mapping. The RH map and the contig map are concordant.