A plea is made for routine use of X-rays in antenatal work. A new method of cephalometry is described, depending on the fact that the foetal head is a rough ovoid. It is shown that the shadows cast by ovoids may be oval or circular, but that always the diameter of the greatest circular section of an ovoid is represented in its shadow-by the diameter if the shadow be circular or by the short axis if oval. The results are applied to estimate the actual proportions of foetal head and maternal pelvis, and also to estimate foetal maturity.The accuracy of the method of cephalometry was tested in 100 cases of labour induced by rupture of membranes.A simple method of pelvimetry is described, and it is suggested that pelvimetry should be carried out in the early months and not later when the pelvis is obscured.No special apparatus is required and any cottage-hospital X-ray set will serve.