Preeclampsia is a pregnancy-specific condition that increases maternal and infant mortality and morbidity. It is diagnosed based on a triad of hypertension, significant proteinuria and rapidly increasing edema during gestation. The factors that initiate preeclampsia are unknown and still a subject of intense clinical research. The objective of this study is to provide additional immunological information about preeclampsia. To achieve this, humoral immunochemical parameters such as three classes of immunoglobulin (IgA, IgG and IgM) and three acute phase proteins (alpha 2-macroglobulin, haptoglobin and transferrin) were measured by single radial immunodifussion method in 32 pregnant women with preeclampsia, 36 pregnant women without preeclampsia and 24 non-pregnant women (controls). Total protein in the urine was also determined by spectrophotometric method. In women with preeclampsia, the levels of IgG, IgA, transferrin and alpha 2-macroglobulin were significantly reduced compared with subjects with normal pregnancy, but the level of haptoglobin was significantly raised in preeclampsia compared with women having normal pregnancy. Urinary total protein and IgG were significantly raised in Nigerian women with preeclampsia compared with non-pregnant controls. There were significant negative correlations between serum IgG, IgA and urinary protein. The possible involvement of immunoglobulins and acute phase proteins in preeclampsia is discussed.