Fifty novel sequenced-tagged sites (STSs) were identified from cosmid clones mapped to human chromosome 11. DNA sequences were determined for one or both cloning ends of 69 cosmid markers that had each been localized to 1 of 24 subchromosomal regions by means of hybridization to somatic cell hybrid panels. Proper primer sequences and appropriate conditions for a polymerase chain reaction (PCR) were determined for each marker. Twenty-one of the cosmids were not suitable for generating STSs, mainly because both of their ends contained repetitive elements such as Alu and L1 sequences; however, some were inappropriate because the sizes of their PCR products from human DNA, used as template, were same as those from yeast DNA. Finally, 50 STSs were established from 48 clones: 20 were derived from markers localized on the short arm and 30 from the long arm. These STSs can serve as new reagents for investigating human DNA in somatic cell hybrids and for isolating yeast artificial chromosomes to anchor large DNA contigs and fine-scale physical maps of chromosome 11.