In order to obtain reference values during normal pregnancy 24 women with strict criteria for health and normal pregnancy were studied. Greatest interest was focused on blood pressure (BP) measurements and renal function tests. Investigations were made in early second trimester and in the 30th, 33rd and 36th gestational weeks. Gestational age was estimated by ultrasound measurement of crown-rump length before the 14th gestational week. Both systolic and diastolic BP measured in the right arm were about 10 mmHg lower in the left lateral position than when supine or standing. The difference is suggested to be dependent on hydrostatic factors. Diastolic BP should be defined at the fourth phase of the Korotkoff sounds in order to be reliable because of the common phenomenon of late or non-disappearance of the sounds during pregnancy. Diastolic BP in phase IV increased in up to 25% of the cases with 15 mmHg or more from early second trimester to the 36th gestational week in all three positions. Serum creatinine concentration was low in early second trimester and did not change during pregnancy, while serum urea decreased and serum urate increased during pregnancy. The results emphasize the importance of using reference values from a normal pregnant population obtained at different gestational weeks for comparison in studies on certain pathological conditions during pregnancy, especially pre-eclampsia.