The presence and diversity of class 1 integrase gene (intI) sequences were evaluated by PCR using previously designed primers. Two clone libraries were constructed from DNA in sediment and microbial mat samples collected on Fildes Peninsula, King George Island, Antarctica.The libraries constructed from samples collected at Halfthree Point (HP) and Norma Cove (NC) contained 62 and 36 partial intI sequences, respectively. These sequences clustered into 10 different groups with <95% amino acid identity. Alignment of the deduced amino acid sequences with those from recognized integron-encoded integrases demonstrated the presence of highly conserved motifs characteristic of intI integrases. The HP library contained 42 nucleotide sequences identical to the class 1 intI gene found in a collection of trimethoprim-resistant (Tmpr) Antarctic Enterobacter sp. isolates, previously collected in the same area. These integrons, located on plasmids, had a genetic organization similar to that of pKOX105 from Klebsiella oxytoca. The 20 remaining HP and NC library sequences were similar to integrase sequences previously determined in a metagenomic analysis of environmental samples. We have demonstrated the presence of integron integrase genes in Antarctic sediment samples. About half these genes were very similar to the class 1 integrons found in humanassociated microbiota, suggesting that they originated from human-dominated ecosystems. The remaining integrase genes were probably associated with endemic bacteria.