The central epidemiologic features of subacute sclerosing panencephalitis (SSPE)--young age of measles attack and overrepresentation or males--are usually explained as resulting from age- and sex-dependent host reactions. In this report, an alternative hypothesis is offered: intensive exposure, presumably due to the dose of infection, is a risk factor in the pathogenesis of SSPE. A hypothetical model of the influence of age and sex on the transmission of measles is suggested. According to this model, girls are exposed to measles more easily outside the home. Furthermore, small children are most likely to be exposed to measles at home. Consistent with this model is the fact that all studies indicate that female SSPE patients contract measles at a younger age than do male patients. Reports in the epidemiologic literature suggest that several characteristics of SSPE may result not from host reactions per se but from the distribution of intensive exposure to measles.