Scent marking activity was monitored at 3 beaver family sites located on Prescott Peninsula, Quabbin Reservation, New Salem, Massachusetts, in 1977 and 1978. A total of 817 scent mounds and 1793 re-marks were recorded at 3 family sites during the 2 year study. Marking activity was highest from March through June, but with wide daily fluctuations. Re-marking of existing mounds became the major marking mode once mounds had been positioned throughout the occupied area. Beaver were opportunistic in choosing both the substrate on which to build a mound and the builidng materials used. Height of the mounds above water appeared to be more critical to beaver than the distance mounds were located from water. Some scent mounds were re-marked over 20 times. Mounds were distributed throughout the occupied area of a family site in an aggregated pattern. The effect of environmental factors on scent marking primarily reflected the seasonal trend in marking. Two major factors, precipitation and a decrease in water level, were identified as modifying this steady seasonal decline, however; both resulted in increased scent marking activity. Castor and anal glands were collected from trapped nuisance beaver. Both glands increased in weight with increasing age and body weight of the beaver and were smaller in females. Anal glands varied in weight during the year, being heaviest in spring and lightest in summer. A theory as to the 'multi-function' of scent marks is presented based on the results of this study and those of previous studies.