Alport’s syndrome is a glomerulopathy of unknown pathogenesis that should be considered in any patient with unexplained hematuria. Four new kindreds of carefully studied family backgrounds were investigated; renal functional tests, otorhinolaryngological and ophthalmological tests, chromosomal maps, light and immunofluorescent microscopic studies were carried out. Renal biopsies of three male patients were also examined by electron microscopy. Characteristic ultrastructural lesions were found: the basement membrane showed segmentary thickenings with characteristic focal and local splitting of the lamina densa, giving rise to electron-lucent space