In 1991, 408 burials of 18th century enslaved Africans were discovered in lower Manhattan. We have analyzed 87Sr/86Sr in tooth enamel and dentine from 31 of these individuals as well as in two burials and the local well water from near Elmina, Ghana a major slave shipment port. Since 87Sr/86Sr is particularly high in the ancient high Rb/Sr cratons of west Africa, Sr isotopes may distinguish New York-born from African-born individuals. 19 individuals in our sample display decoratively filed teeth, an African custom believed to have been repressed in the New World. The remaining 12 individuals are young (< 25 years old at death) and lack decorative modification. This later group displays tightly clustered 87Sr/86Sr in first molar dentine and enamel (~0.71159 +/-0.00072), apparently the indigenous NYC value. This group may comprise native New Yorkers. The remaining nineteen with decorative teeth show enamel 87Sr/86Sr ranging widely (0.7085 to 0.7275). Sixteen of the modified group show dentine 87Sr/86Sr generally quite unlike that in their enamel, and closer than their enamel to 0.71159 whether their enamel fell above or below that value (avg dentine: 0.71240+/-0.00185). Two modified individuals have the NYC value, and one (#165) shows enamel ~0.718 and dentine ~0.719. The enamel-dentine differences may be due to recalcification of dentine during later life, and/or to diagenetic alteration after death. If, as suggested by #165's result, recalcification during life is more important, a rough estimate of residence time in NYC may be derived from the proximity of the dentine 87Sr/86Sr to 0.71159 relative to the enamel value. At 0.7355, the Ghanian well water is our highest measured ratio. Ghanian dentines show 87Sr/86Sr closer to 0.7355 than their corresponding enamel, also suggesting that these individuals were not native to their burial place.