The serum levels of alpha2-macroglobulin (alpha2-MG) were determined by radial diffusion if fifty-four cases with tuberose sclerosis and compared with forty-seven institutionalised control subjects of similar age and sex distribution. Although higher levels of alpha2-MG were found in the females of both groups when compared with the males, this increase was not significant. The tuberose sclerosis subjects showed consistently elevated levels of alpha2-MG when compared to the control group for both the males and females separately and combined. With the two sexes combined this elevation was significant at p less than 0.001. The significance of this observation has been discussed both from the point of view of the possible mechanism involved and the use of this estimation in genetical counselling.