Henderson, R. H. (Smallpox Eradication Program, NCDC, Atlanta, Ga. 30333) and M. Yekpe. Smallpox transmission in Southern Dahomey. A study of a village outbreak. Amer. J. Epid., 1969, 90; 423–428.—An outbreak of 28 cases of smallpox which lasted for over three months was studied in a village of 300 persons in Southern Dahomey. A striking geographic localization of cases was observed within the village and appeared to reflect the intimacy of contact which existed between persons inhabiting the affected households. This localization could not be related to differences in vaccination scar rates which existed between the affected households and the village at large. Although the village was vaccinated at the time of the investigation, it is probable that the outbreak had terminated before these vaccinations were given. Smallpox transmission appeared to stop when the supply of susceptible in prolonged intimate contact with the cases was exhausted, but when susceptibles who were in casual contact with the cases were abundant in the village. The observed behavior of smallpox in this outbreak suggests that transmission occurring from casual contact is a rare event, but also suggests that it can be sustained over long periods in small population groups. Calculation of the number of smallpox transmissions which occurred per 100 susceptible household exposures suggested that the infectivity of smallpox is greater than that of mumps, but less than that of chlckenpox and measles.