Well-preserved skeletons of 50 Dutch whalers from the 17th and 18th centuries, buried on the island of Zeeusche Uytkyck , were excavated during the Spitsbergen Expedition 1980. In order to estimate the biological age of these skeletons at the time that Harris's lines were formed, a method which was developed from routine X-ray data on tibial growth was tested. Formation ages of diaphyseal lines and strong metaphyseal lines appear to correspond well with hypoplastic enamel deformations within the same individuals. Because of the involvement of both the bone and tooth developmental systems, and of the resistance of these lines to bone remodeling, it can be assumed that they generally are the result of serious health insults.