1. A modification of Gustafson's method is described with a view to estimating individual age according to the state of teeth in prehistoric bone material. Age estimation is made on he basis of a hisological investigation of the hard dental tissue and of the changes that affect teeth as the individual grows old. 4 markers are ascertained on thick sagittal sections of singleroot teeth in prehistorical material: degree of dental abrasion, secondary dentin desposition, cement aposition, and dental apex resorption [Fig. 1.], with scores ranging from 0--3 points. Using the marker system described by Gustafson the corresponding average age values were estimated for the total scores of the 4 markers ascertained [Fig. 2, Tab. 1] and the standard error of estimation was calculated [Tab. 2]. 2. The above method helped to estimated the age of Czech Princes ruling at the turn of the 9th and 10th centruies, whose remains were discovereed at Prague Castle. The age of Prince K 1 was thus estimated at 30--35 years, that of St. Wenceslaus at 40--45 years, and that of he Prince of Zizi at +/- 60 years. 3. The modification makes it possible for anthropologists and forensic experts to use the histological method of Gustafson's section in estimating the age both in prehistorical and in recent bone material.