A solution to the controversy on stem cell regulation.

Supplementary to the discussion in Blood Cells 7 (1981) pp. 417-443 concerning regulatory mechanisms of stem cell proliferation and differentiation, the consequences of the two proposed hypotheses of Blackett and Botnick and Lord have been calculated. It can be shown that their equations are equivalent and can be transformed into each other. However, their verbally described regulatory mechanisms are different and turn out to be more important than the equations. The assumptions of Blackett and Botnick lead to an unstable behaviour of the stem cell system with cyclic cell numbers while the hypothesis of Lord leads to stable recovery curves.