This paper describes the reconstruction of the remodelling cycle in normal iliac crest cortical bone from static and dynamic variables after double labelling with tetracycline in 10 young normal individuals. The average duration of the resorptive period was 27 days during which the average rate of resorption was 4.7 microns/day. The final resorption depth was 76 microns. The diameter of osteoclast containing cutting cones was significantly smaller (P less than 0.05) than cutting cones containing mononuclear cells, indicating an initial osteoclastic resorption phase preceding a mononuclear resorption phase. The average mineralization lag-time was 8 days and the formative period 89 days. Osteoid thickness during this period averaged 5.8 microns. The seam thickness varied with the underlying uncompleted wall thickness, i.e., during the course of the formative period, with matrix deposition initially exceeding, later equalling and finally lower than the rate of mineralization. The mineral appositional rate (MAR) was 1.2 microns/day and the adjusted mineral appositional rate (Aj.AR) 0.9 micron/day. Both MAR and Aj.AR decreased during the formative period. A completed wall thickness of 62 microns left a Haversian canal with a diameter of 29 microns. After a quiescent period of 438 days the osteon (or parts of it) was reactivated. The average activation frequency was 0.93 per year.