The carbon and oxygen isotopic composition of the mineral phase of tooth enamel is linked to diet and environment. Enamel is not remodelled once formed. Several studies of intra-tooth isotopic variability in hypsodont mammal teeth have involved sequential sampling of enamel in order to detect changes in diet and environment during tooth formation. The possibility of exploring individual history opens the door to many applications, particularly in palaeoenvironment and herd management reconstruction. However, previous histological investigations have shown that enamel mineralization is a progressive and discontinuous process. The goal of the present study is to determine if this pattern significantly influences the time resolution of an intra-tooth sequential sampling. Isotopic analyses (δ13C) were performed on tooth enamel from steers (Bos taurus) that had changed from a C3 plant-based diet to a C4 plant-based diet with very different carbon isotopic compositions. The change of diet was reflected in the mineral phase of enamel. The pattern of intra-tooth isotopic variation suggests that completion of enamel mineralization required six to seven months. Such a lag in enamel mineralization will decrease the time resolution of enamel sequential sampling. The effects of prolonged mineralization of enamel have to be considered when interpreting patterns of intra-tooth isotopic variations. Copyright © 2002 John Wiley & Sons, Ltd.