During the 1972 growing season, the productivity of a short form and a tall form ofSpartina alterniflora was studied by the harvest method in the vicinity of the Rutgers Marine Sciences Center on Great Bay near Tuckerton, New Jersey. The aboveground biomass of living and dead grass was determined and subsamples were analyzed for caloric equivalents, ash, nitrogen, crude protein, crude fiber, ether extract, and nitrogen free extract. S. alterniflora had peak standing crops of 1,592 g/m2 for tall form and 592 g/m2 for short form. Standing crops of crude fiber, ether extract, nitrogen free extract, and caloric values are a function of dry matter production while nitrogen components seem to be influenced by some other factor. Seventy percent of the crude protein was present in early summer at a time when dry weight was less than 50% of its maximum value. The data indicate that the amount of nitrogen that the plant accumulates in its aboveground parts early in the growing season is directly related to the peak of dry matter standing crop. The early spring accumulation of nitrogen may act to offset shortages at the peak of the growing season. The chemical composition of litter and soil samples suggests that biological breakdown of plant material occurs at the soil surface.