We measured plasma Cu. Zn and Mg levels in 40 women suffering from premenstrual tension syndrome (PMTS) and in 20 control subjects by atomic absorption spectrophotometer. Mean plasma Cu, Zn and Mg levels, the Zn/Cu ratio were 80.2 +/- 6.00 micrograms/dl, 112.6 +/- 8.35 micrograms/dl, 0.70 +/- 0.18 mmol/l, and 1.40 +/- 0.10 in the PMTS group; and 77.0 +/- 4.50 micrograms/dl, 117.4 +/- 9.50 micrograms/dl, 0.87 +/- 0.10 mmol/l, and 1.51 +/- 0.05 in the control group respectively. The mean Mg level and the Zn/Cu ratio were significantly lower in PMTS patients than in the control group. Plasma Mg and Zn levels were diminished significantly during the luteal phase compared to the follicular phase in PMTS group. Mg deficiency may play a role in the etiology of PMTS.