I. Introduction, 413. — II. A model of cash flows and the costs of cash management for business firms, 416; assumptions underlying the model, 417; optimal values of the policy parameters, 420; some properties of the solution, 423; implications for the demand for money by firms, 425; extension to allow for non-zero drift, 427.— III. The applicability of the model, 429. — Appendix, 433.