Analysis of DNA from Aegilops tauschii revealed that sequences hybridisable to the starch branching enzyme I (SBE I) gene were contained within a 53-kb fragment. There were at least four genes or gene fragments but of these only one appeared to encode the SBE I observed in the endosperm. Two large-insert DNA clones that encode SBE I from A. tauschii were isolated. Hybridisation analysis confirmed the presence of multiple SBE I gene type sequences within this DNA fragment of approximately 100 kb. Fluorescent in situ hybridisation (FISH) on extended DNA fibres provided further evidence of the close proximity of three of these genes. Sequence analysis was undertaken and this demonstrated that wSBE I-D3, wSBE I-D2 and wSBE I-D4 genes were clustered within 27 kb of DNA; of these only wSBE I-D4 encodes the SBE I purified from the endosperm. Multiple but distinct cDNAs containing SBE I-related sequences have been reported and these could arise from the SBE I locus by different transcription/splicing regimes.