A wide range of objects have been designed to attract tsetse, such as simple cloth screens, or to both attract and catch them, traps of varying degrees of complexity. The shape and size of these objects affect the number of flies that are attracted to their vicinity and those that actually alight on them or, in the case of traps, are caught by them. Studies on the spectral responses of male Glossina morsitans morsitans, using electrophysiological and behavioural techniques, have shown response maxima in the u.v. and in areas of the visible range. Preliminary field studies are described, in which performances of traps covered in different coloured materials of known spectral reflectance were assessed. The most important colour determinant of trap score is the proportion of attractive blue (400–500 nm) to unattractive green-yellow (500–600 nm) in the reflectance of the material used. Reflectivity of red (above 600 nm) is also a positive factor in trap attractiveness. Optimising the visual attractiveness of targets is particularly important if odour is not employed to effect the initial attraction of tsetse to their vicinity.