Smith C E [Department of Biometry, Medical University of South Carolina, 171 Ashley Avenue, Charleston S C 29425. USA]. The Broadstreet pump revisited. International Journal of Epidemiology 1982, 11: 99–100. This historical note examines the effect of population migration on the number of fatal cholera cases reported by John Snow in the Golden Square area of London during the fall of 1854. A method to correct for population migration is given and its relevance to present day epidemiological studies discussed.