Light microscopy was used to scan thin ground sections of first molars (M1), third molars (M3), and second premolars (P2) to determine relative amounts of interglobular dentin (IGD) in the top half of the crown. Samples were taken from two well-dated cemeteries of English provenance, 18th century; sex, age, and calendar year of death were clearly known for each specimen. The second site was Anglo-Saxon, near Abingdon. A small number of pre-Hispanic aboriginal Guanche teeth from Tenerife was also included in the study. Estimates of past in solation were indirectly developed using as reference Á9₁₈O mass spectrometer analyses of dated layers of the Greenland ice sheet. Within the English samples the IGD varied as an inverse linear function of average annual hours of bright sunlight below a certain critical level, the insolation deficit threshold being higher and IGD formation faster in the M1 than in the M3. The P2 data showed no similar dose-response gradient, possibly because the calcification of this tooth during the fourth year of life coincides with major pediatric illnesses and weaning of the child onto cereal foods rich in phytate, which negate the effects of the insolation deficit. IGD in all three types of teeth of the Guanche group was considerably higher than what would have been predicted based upon the availability of sunlight; this discrepancy is explained by the population's diet, barley being the main staple. -- AATA