The "in vitro" cellular growth of 8 amniotic membranes from preterm deliveries with premature rupture of membrane (PROM) in absence of risk factors as cervical or vaginal infection (microbiologic negativity), cervical incontinence and other mechanical factors, was compared with cellular growth of 9 amnions from preterm deliveries without PROM. Amniotic membranes were set up in the Eagle basal medium with Earle salts and heat-inactivated fetal bovine serum (10%), gentamicin 50 micrograms/ml and amphotericin B 0.5 micrograms/ml. The results suggested that the growth potential of the cells (epithelial cells and fibroblasts) obtained from amnions with PROM was lower than that of cells obtained from amnions without PROM. We postulated that the premature rupture of membranes in patients without risk factors for PROM, would be conditioned by an intrinsic decrease of cellular growth potential.