A relationship was sought between renal hyperechogenicity and the hypoxic state of fetuses. 120 pathological pregnancies were examined between the 28th and 36th week. All of these women exhibited moderately increased levels of hepatic enzymes, 3 of them had a pathological kidney function, and 4 of them displayed hyperuricemia during the examination period. The echogenicity of the fetal kidneys was examined with Hitachi EUB-450 ultrasound equipment with a 3.5 MHz transducer. The kidney (creatinine, urea-N, uric acid, triglyceride, cholsterin) and liver (SGOT, SGPT, GGT, bilirubin) functions and plasma electrolytes (Na, K, Ca, Cl) of the mothers were also examined and blood was collected from the pulsating umbilical artery for determination of the same parameters. After delivery, the physical condition of the neonates was followed and their kidneys were examined with the same ultrasound equipment within the first 5 days. There was a significant correlation between a pathological neonatal clinical outcome and the frequency of fetal and hyperechogenicity (chi-square test with Yates correction, p < 0.01). The results demonstrate that fetuses exhibiting renal hyperechogenicity in pathological pregnancies require particularly careful obstetric control and neonatological consultation. It is important that hyperechogenic cases be admitted to a perinatal intensive care unit. Fetal renal hyperechogenicity is considered to be associated with an enhanced risk of an adverse perinatal outcome.