Microscopic sections of 37 temporal bones from 22 foetuses were examined, five with renal agenesis, six with Potter's sequence without renal agenesis and two with mild kidney pathology. Every tenth section containing the stapes were used for measuring the volume of mesenchymal tissue in the middle ear cavity. At 5% significance level, foetuses with serious renal pathology had more mesenchymal tissue in the middle ear cavity than a control group of nine foetuses with no renal or urinary tract abnormality.