In 228 pregnant women examined by ultrasound in the 30th to the 40th week of gestation, the first placental maturity degree was found in the 31.6 week, the second degree in the 35.8 week, and the third degree in the 38.2 week. In 60 women with on term pregnancy also amniocentesis was carried out and the lecithin-sphingomyelin ratio (L/S) was compared with the ultrasound finding. In 6 of these pregnant women the third degree of placental maturity was observed, their L/S ratio was not below 2, and in their newborns no respiratory distress syndrome developed. Ultrasound estimation of placental maturity is a useful method in pregnancies in which no other methods could be applied.