Hyperhomocysteinemia has been associated with several pregnancy complications. We have investigated the variation of plasma total homocysteine (tHcys) during the 2 last trimesters of normal pregnancy and related it to blood vitamin B12 and folate and to the excretion of the degraded intrinsic factor receptor (IFCR) in urine, in a follow-up study of 15 cases. A significant rise in tHcys was observed between the beginning of the second trimester and the third trimester with respective values (median) 6.1, 5.8 and 6.7 micromol/l (p = 0.038). The tHcys/albumin ratio also increased significantly, while no correlation was found between albumin and folate blood concentration. In contrast, a significant decrease in vitamin B12 was observed (279, 225 and 199 pmol/l, between the 4th and 6th, and the 6th and 9th month, respectively (p = 0.017-0.002)). A significant negative correlation was found between tHcys between the 4th and 9th month of pregnancy and the ratio of vitamin B12 between the 4th and 9th month of pregnancy (r = 0.55, p = 0.037). The urine excretion of IFCR was increased and was not related to vitamin B12 and tHcys. In conclusion, we have observed a rise in tHcys between the beginning of the second trimester and the third trimester of pregnancy which was related to the decreased blood level of vitamin B12. Subclinical deficiency of vitamin B12 should be further investigated in pregnant women who remain on inadequate diet.