An Analogue Model of Granulopoiesis for the Analysis of Isotopic and Other Data Obtained in the Non‐steady State

S ummary . An analogue model of human granulopoiesis incorporating feedback control is presented which is less restricted than previous models. The model simulates kinetic data from human DF 32 P and 3 H‐thymidine labelling experiments, and the data obtained by Morley & Stohlman in mice (1970) following destruction of four‐fifths of the marrow. Support for King‐Smith & Morley's (1970) suggestion that cyclic neutropenia may be a stem cell defect is forthcoming, but only after the addition of a further negative feedback loop simulating a granulocyte‘chalone’ or a considerable reduction in the time required for precursor cell division. The value of the model in the interpretation and design of kinetic studies, particularly in the non‐steady state, is discussed.