Studies were undertaken to determine the relationship between size of northern quahogs Mercenaria mercenaria and the rate at which they transport aspartic acid. Quahogs ranging from 25 to 103 mm valve length were collected in Narragansett Bay and placed in seawater aquaria (27 ppt, 20 deg C) and allowed to pump actively. Uptake experiments were carried out using 1 umol/L C(14) radiolabeled aspartic acid. Aspartate transport rates in umol/h can be related to valve length by the allometric equation with a = 24.32 and b = 0.905 when valve length is in mm. In May 1990, near bottom samples of seawater ere taken from five locations in Narragansett Bay for analysis of dissolved free amino acids (DFAA ) by high-pressure liquid chomatography. Rsults show tha the mean total DFAA was 667.6 nmol/L +/- 167.3 SD, with the top five being serine, alanine, aspartic acid, glutamic acid, and glycine. A simple spreadsheet model was used to assess the relative importance of uptake of DFAA vis-a-vis the filtration of particulate matter by M. mercenaria. In the model, environmental DFAA concentrations and uptake rates by quahogs determined in this study are compared to literature values of particulate organic nitrogen concentrations and filtration rates by quahogs. On an annual basis, uptake of DFAA can account fot about 14% of the total organic nitrogen uptake by quahogs. Uptake of DFAA by these benthic filter feeders may be a pathway of benthic-pelagic coupling that is often overlooked in coastal ecosystem analysis.