Plasma urea concentrations were determined for 109 pregnant Caucasian women and 117 pregnant urban African women covering the last two trimesters of pregnancy. Elevation of the urea level was observed in both populations. The elevation was progressive in both cases. The urea levels for Caucasians were apparently normal until about the thirteenth week of gestation when it rose to above normal level and increased progressively in the third trimester. For the Africans, the progressive rise was similar but the values did not exceed the normal range until after the thirty-second week of gestation. Thus, a general pattern of variation which is similar in both Caucasians and Africans exists for the plasma urea level during pregnancy. However, the levels for Caucasians over the gestational periods are consistently higher than the level for Africans. The increase in the level of this non-protein nitrogen compound was attributed to increased intake of proteinous foods and is probably a result of diminished excretion of urea arising from pre-renal causes such as volume depletion.