Blood and plasma viscosity, fibrinogen concentrations and whole blood filterability (VB) were evaluated before surgery and 7 and 30 days postoperatively in 2 groups of subjects, one of which comprised 10 hysterectomized women and the other 14 women who had undergone both hysterectomy and ovariectomy. Oestrogens and various metabolic haematological parameters were measured and correlated with the haemorrheological data. By day 7 after surgery fibrinogen concentrations and plasma viscosity had increased, while VB had decreased. Plasma viscosity and fibrinogen levels correlated negatively with VB in the non-ovariectomized women. Three weeks later almost complete normalization of all parameters was observed in all of the subjects, except for the persistence of low oestrogen concentrations and a further decrease in VB values in the ovariectomized patients, these parameters showing a positive correlation. This study demonstrates that haemorrheological alterations occur after hysterectomy (with or without ovariectomy) in the early post-operative period. The striking decrease in VB values and its correlation with the oestrogen concentrations observed 1 mth after ovariectomy suggest that the fall in oestrogen levels might be responsible for the decrease in whole blood filterability.