The ability of 17α-ethinylestradiol (EE2) to elevate vitellogenin levels were investigated in male flounder Platichthys flesus and vitellogenin concentrations in flounders from the Danish coastal environment were determined. Male flounders were exposed to 17α-ethinylestradiol (EE2) via food or water. Average vitellogenin concentrations in the control fish ranged between 25 and 100ngmL -1. Exposure to 5.1, 8.1 and 16.8ng EE2 L -1 in water and 500 and 5000ng EE2 kg -1 body weight (bw) every second day in the food increased the plasma vitellogenin concentration in a concentration and time dependent manner, whereas exposure to 2.7ng EE2 L -1 in water for 21d and 5 and 50ng EE2 kg -1 bw for 12 days in the food did not. EE2 could be detected in liver and testes (but not in muscle) after exposure to 8.1 and 16.8ng EE2 L -1 in the water and 5000ng EE2 kg -1 bw in the food; the highest concentration was 6ng g -1 wet weight in liver. The majority of the male flounders collected from nine coastal Danish sites from 1999 to 2004 had vitellogenin concentrations below 100ngmL -1, and only at two sites moderate estrogenic inputs were indicated.