Early release of mature bone marrow granulocytes either with ‘empty’ stores or with exaggerated turnover rate of the marrow store furnishes more alkaline phosphatase positive neutrophils, whereas release of already stored cells furnishes more alkaline phosphatase negative cells. Thus, providing other factors, such as release of splenic or marginal granulocytes, do not disturb the condition, neutrophil alkaline phosphatase activity appears to reflect the bone marrow retention of candidate cells. The biphasic response to adrenal steroids could be explained by this hypothesis