Holoprosencephaly (HPE) is a developmental field defect involving the brain and face. Cytogenetic deletions in patients with HPE have localized one of the HPE genes to chromosomal region 7q36. We have characterized the 7q deletions in thirteen HPE patients. The result is the construction of a high resolution physical map of 7q32-qter. As a first step towards cloning an HPE gene crucial for normal brain development, we have defined the HPE minimal critical region in 7q36 between D7S292 and D7S392.