Recent evidence indicates that avian embryonic exposure to polychlorinated dibenzodioxins (PCDDs) and related compounds is associated with the development of a gross brain asymmetry which can be quantified. Three methods can be used to quantify the asymmetry,including external measurements of the intact brain, measurements of brain cross-sections and measurements of computer tomography (CT) - generated images of brain sections. All three methods produce reliable results. The whole brain measurements do not require specialized equipment, and are the most flexible. However, the possibility for unintentional bias is greatest for this technique. The CT scan technology is non-invasive, but requires access to specialized equipment and may be expensive. The cross-sectional measurements, which are similar to the CT scan measurements, require careful processing prior to measurement.