The hypothesis that oral tyramine causes migraine headache in certain patients was proposed by Hanington in 1967. In all, there are 11 published reports that experimentally test the hypothesis. Six of these studies provide support for the hypothesis whereas the results of four studies are clearly not supportive. All of the supporting evidence was generated in one laboratory (Hanington). In an attempt to evaluate this conflicting evidence, a comparison was made of outcome measures, subject selection procedures, and various methodological differences. There were some anomalous findings, most notably that there were marked differences in "placebo" headaches elicited by lactose capsules from study to study. Further, methodological differences among the studies preclude direct comparisons of the results. Taking these differences into account, the tyramine hypothesis appears to have some validity. The implications of these findings were discussed.