Malformations of the intestinal tube were studied in 220 infants and in 15 human embryos. Comparison with data in the literature allowed that atresias, stenoses and duplications of the gastrointestinal tract result from some primary morphogenetic disturbance in early gestation more often than from a failure of recanalization, interference with blood supply in fetal life, or from enteritis or peritonitis. This is based on the association of these defects with chromosomal abnormalities (trisomies, partial monosomies, etc); association with malformations which cannot be explained by secondary lesions; the finding of oesophageal stenosis in 6 week-old embryo prior to the stage of epithelial proliferation; the lack of vascular disturbance in cases of the "apple-peel" syndrome and persistence of intramural ganglia in affected segments of bowel.