OBJECTIVE To determine a relationship between gestational age and the quantitative assessment of ultrasonic signs of placental tissue, fetal lung and liver tissue for determining fetal lung maturity in normal pregnancies and pregnancies with preeclampsia. METHODS Placental, fetal lung and fetal liver tissue was examined by ultrasound in 240 normal and 60 preeclamptic pregnancies at 30-41 weeks' gestation. All patients underwent ultrasonically guided amniocentesis to obtain the lecithin-sphingomyelin ratio. The placentas of 160 patients after delivery were placed in water at body temperature for ultrasonic echo amplitude analysis. The coefficients of variation (the standard deviation divided by the mean value) of gray levels of the pixels in the region of interest obtained from images of the placenta, fetal liver and lung, were used to characterize the tissue in different groups during pregnancy. RESULTS The coefficients of variation in mature fetuses were > 29% for placentas in vivo, > 34% for placentas in vitro, > 28% for liver tissue and > 30% for lung tissue. In mature fetuses the ratio of coefficients of variation of placental tissue in vivo against placental tissue in vitro was > 0.80, placental tissue in vivo against lung tissue > 0.90, lung tissue against liver tissue > 1.10 and placental tissue in vivo against liver tissue > 1.00. CONCLUSIONS The placental and fetal lung tissue of preeclamptic patients tended to have higher coefficients of variation throughout pregnancy. These results were significantly higher when associated with low-birth-weight babies. There were no significant differences in fetal liver tissue between normotensive and preeclamptic groups.