BACKGROUND Two possible factors that may have a causal relation with both depressive disorder and cardiovascular disease are elevated homocysteine and steroid hormones. Our previous study found significant changes in the plasma homocysteine concentration during the menstrual cycle in healthy women. The purpose of this study therefore was to test homocysteine in depressive women treated with fluoxetine during the menstrual cycle. METHODS Thirteen premenopausal women suffering from mixed anxiety-depressive disorder and a control group of 15 healthy women were enrolled in this study. The homocysteine concentration was determined by high-performance liquid chromatography with fluorescence detection, and estradiol, progesterone and cortisol by RIA methods. RESULTS We found significantly higher plasma homocysteine concentrations in the follicular phase than in the luteal phase of the menstrual cycle in both the depressive group (P < 0.003) and the controls (P < 0.0009). Moreover, the patient values of total homocysteine were significantly higher in the follicular phase (P < 0.03) and also in the luteal phase (P < 0.007) than the values of the controls. Estradiol and cortisol were significantly higher in the follicular phase of the patients compared with the control group. CONCLUSIONS According to our results, women suffering from mixed anxiety-depressive disorder have not only significantly different concentrations of homocysteine in the follicular and luteal phase of the menstrual cycle but also higher plasma homocysteine compared with healthy women. More elevated homocysteine in the depressive than in the healthy premenopausal women points to the notion that psychological factors might be important when considering the homocysteine concentration.