Abstract
Data on pyloric stenosis are analysed by multiple threshold methods that incorporate the sex effect. The polygenic model of inheritance is rejected; the single major locus model can only account for 37% of the cases having a genetic aetiology, requiring an environmental effect to account for the remainder of the cases. A maternal-fetal interaction for gastrin production and sensitivity is postulated to explain all the existing data. The empirical risk figures given are considered to be the most accurate basis for genetic counselling until additional studies provide a sound biological basis for a quantitative genetic model.