S2Some maple sap producers have wondered whether they could increase the total sap yields by tapping their trees not only in the spring but also in the fall too. Our research indicates that tapping in the fall cannot be recommended. Our study of fall tapping was begun in November 1964. Fall tapping was at least theoretically possible because temperature fluctuations like those of the normal spring tapping season occur to some extent in late fall and early winter. However, it was not known whether the volume and sugar concentration of fall-produced sap would be adequate to make such a practice feasible. Nor did we know whether fall tapping would affect the normal spring sap production from fall-tapped trees. The study reported here was set up to answer these questions. S3.