An exposure chamber, the 'clambox', was developed to measure ventilation rate, sediment processing rate, and efficiency of pollutant uptake by Macoma nasuta, Conrad, a surfacedeposit-feeding clam. Clams, collected from Yaquina Bay, Oregon, USA, were cemented into a hole in a piece of rubber dental dam so that the inhalant siphons were separated by a membrane. The dental dam was then clamped between two glass chambers. The inhalant and exhalant siphons were thus diirected into separate chambersof the device so that the amount of water or feces discharged into the exhalant camber provided direct measure ventilation rate and sediment processing rate, respectively. The shor-term pattern was for ventilation to be intermittently interrupted, essentially ceasing for 12 to 120 min, followed by a short period of active ventilation and thhen a resumption of the normal rate.