The study found that a large-scale latitudinal relationship between mammalian tooth enamel d18O values exists and that this relationship can be tracked spatially along a global latitudinal gradient. Also, the values observed for the United Kingdom were constrained between -8.5 to -4.08d18O. This shows that a United Kingdom range can be defined for "exclusion," i.e., that values which fall outside the United Kingdom range must pertain to individuals who, during the period of tooth formation, were living at either a more northern or southern locale with respect to the United Kingdom. Much research remains to be done on this issue, but it is envisioned that oxygen depletion and enrichment geographical data can contribute one piece of life history for skeletal and other human tissue. This study used modern horse molars and human molar tooth extractions. The horse teeth were drawn from a geographical location where horse life history was known during the period of the formation of the teeth sampled. Human teeth were collected from the Natural History Museum in London and were composed of childhood extractions that had been retained. These teeth were donated to the study, and the geographical location of staff was documented for the period of crown formation. The horses' geographical locations were recorded at latitudinally descending locales that extended from Iceland, the United Kingdom, Spain, Greece, Aden, to the Sudan. They were from lowland locations in order to avoid any altitude-temperature effects. The geographical locale for human teeth was limited to the United Kingdom during the period of crown formation. Sampling procedures are described. 2 tables, 2 figures, and 34 locations