The calcification rate and the completed wall thickness of remodeling sites in trabecular bone were estimated in undecalcified sections of tetracycline double-labeled iliac crest bone biopsies from 20 epileptic patients aged 19 to 50 years receiving long-term combined anticonvulsant therapy and 20 age- and sex-matched normal individuals. Surface distributions of thickness were obtained by a systematic equidistant sampling procedure and three-dimensional (3-D) values estimated from the two-dimensional (2-D) measurements by means of a stereologic transformation. The mean 3-D completed wall thickness was slightly reduced (P less than 0.01) in the epileptic patients (58.9 microns as compared to 62.8 microns), while no statistically significant change in the mean 3-D calcification rate (0.62 microns/day as compared to 0.64 microns/day) was found. Surface distributions of wall thickness and calcification rate were unimodal and resembled normal distributions in patients as well as in controls. The estimated duration of the formation period at remodeling sites was almost 4 months for the normal individuals and insignificantly shorter for the epileptic patients. Double determinations after 2 to 3 month intervals revealed no significant intraobserver bias in the estimates of the wall thickness or the calcification rate.