We are applying a transposon-based approach for detecting and mapping features of special interest to construct 'feature maps' of currently uncharacterized portions of the human leukocyte antigen (HLA) complex on chromosome 6. Such feature maps should facilitate identifying regions for high resolution analysis. Here we describe the feature mapping of a 35 kb DNA fragment located between the HLA-C and HLA-E loci. This fragment was cloned into a transposon γδ-based cosmid vector designed for generating nested deletions in vivo. Seventy informative nested deletions extending into the cloned fragment were isolated, and DNA adjacent to the deletion endpoints was sequenced by fluorescent automated technology. These Islands of DNA sequences constituted the foundation of the feature map, and (i) identified putative exons, (ii) determined the positions of Alu elements, (iii) determined the span of the keratinocytespecific S gene, and (iv) localized evolutionarily conserved sequences. The construction of feature maps using this in vivo nested deletion-sequencing approach provides a rapid and efficient means to identify DNA regions that merit more detailed analysis. © 1995 Oxford University Press.