Sera from 176 patients with hypertensive disorders of pregnancy, intrahepatic cholestasis of pregnancy, and oedema of pregnancy, and from 51 normal pregnant control subjects were tested for smooth muscle antibodies (SMA) by indirect immunofluorescence. An increased incidence of SMA positivity was found in cases of pre-eclampsia and in superimposed pre-eclampsia of pregnancy, oedema of pregnancy and intrahepatic cholestasis of pregnancy combined with oedema of pregnancy. In the pre-eclampsia group, SMA positivity occurred only in cases of pre-eclampsia levis and was often accompanied by mild proteinuria. This indicates that SMA are a result rather than a cause of an (immuno)pathological process, the short duration of which in severe forms is not enough for the development of the antibodies. The increased incidence of positive SMA titres in oedematous pregnant patients may be a sign of imminent pre-eclampsia, although oedema is often regarded as being a feature of otherwise normal pregnancies.