Although male UV structural plumage coloration can indicate male quality (e.g. Keyser Hill 2000) and female reproductive investment strategies (e.g. Sheldon et al. 1999, Griffith et al. 2003), unambiguous evidence that such plumage is a direct target of female choice is still lacking. A straightforward way of testing this is by conducting controlled mate choice experiments that exclude confounding factors such as malea??male competition or territory quality. The first experiments on the role of structural colours in mate choice used UVblocking windows (e.g. Bennett et al. 1996, Hunt et al. 1999), thereby completely removing male UV reflectance. A better approach is to vary UV reflectance within the natural range under natural light conditions. Only two such mate choice experiments have been undertaken to date (Ballentine Hill 2003, Liu et al. 2007). In neither study did females show a preference for more UV-ornamented males. In the present study, we manipulated crown reflectance of first-year male Blue Tits Cyanistes caeruleus to test the hypothesis that females prefer males with a higher crown UV reflectance, as predicted by patterns of sex allocation, paternity and female parental investment in this species (Johnsen et al. 2005, Delhey et al. 2007a,b).