In this paper we qualitatively analyze mathematical modeling of the cell di
vision cycle established by Novak and Tyson (Novak B, Tyson JJ. J Theor Bio
l 1993;165:101-34) and discuss the existence, uniqueness, stability and uns
tability of its singular point and the system boundedness, existence and no
nexistence of closed orbit and its global structure. (C) 2000 Elsevier Scie
nce Ltd. All rights reserved.