In previous studies, we found multiple copies of inducible nitric oxide synthase gene (NOS2)-like sequences in the human genome and mapped them to the pericentric region of chromosome 17. Here, we describe the cloning and sequencing of exon22 regions from three of these NOS2-like sequences. We have also mapped another NOS2-like sequence to human chromosome 14. Since there are multiple NOS2-like sequences present in the human genome, we have also carried out Zoo Blot hybridisation analysis using a NOS2 cDNA probe. Our data suggest that duplication of NOS2-like sequences occurred very recently in primate evolution.