The objective of this study was to assess the nutritional adequacy of sub-elite runners with irregular menstrual function (n=10) and that of a comparable group of runners with regular menstrual function (n=10), with a special focus on vitamin E. Based on 3 days' records of weighed dietary intake, the mean energy intakes of micro- and macronutrients were estimated. Both estimated daily energy intake (irregular: 9.9+/-0.4 MJ; regular: 12.2+/-0.7 MJ; mean+/-sx) and intake of dietary fat (irregular: 61+/-6 g; regular: 98+/-12 g) were lower in athletes with irregular menstrual function than in athletes with regular menstrual function (P=0.01). Estimated intake of vitamin E was below recommended values in both groups. Serum concentrations of alpha-tocopherol were used to evaluate vitamin E status, which were normal in athletes with regular menstrual function (27.3+/-3.6 micromol.l(-1)) but below normal values in athletes with irregular menstrual function (15.7+/-0.8 micromol.l(-1); P=0.01). Furthermore, post-exercise osmotic fragility in red blood cells was inversely related to resting alpha-tocopherol concentrations. Our results indicate that irregular menstrual function in athletes on a low-fat diet is associated with low concentrations of circulating alpha-tocopherol, rendering the red blood cells more susceptible to haemolysis in connection with physical activity.