We performed experiments on male Australian painted dragon lizards (Ctenophorus pictus) to test the hypothesis that carotenoids can scavenge reactive oxygen species (ROS), protecting the organism from oxidative stress, and that this capacity is reflected in skin colours involved in signalling. Subsequent to 4 weeks of carotenoid treatment we used flow cytometry to analyse unspecified ROS (H(2)O(2), singlet oxygen, superoxide and peroxynitrite level), hereafter termed ROS, and baseline superoxide specifically (bSO in peripheral blood cells). Mean background levels of ROS and bSO did not differ between carotenoid-treated and control males. bSO, which represents the superoxide level in un-manipulated blood, was negatively correlated with colour development in all males, regardless of carotenoid treatment. Thus, carotenoid intake does not reduce circulating levels of ROS or bSO, suggesting that carotenoids are inefficient antioxidants in vivo and, therefore, are unlikely to provide a direct link between oxidative stress and colouration.