Several configurations of receiving disks and diffusion membranes were tested for monitoring mercury and organotin compounds (monobutyltin, dibutyltin, tributyltin, and triphenyltin) in water with a passive sampler. This passive sampler is based on the diffusion of these compounds through a specific diffusion-limiting membrane and their subsequent accumulation on a specific receiving phase, all materials being commercially available. The proposed sampler for inorganic mercury comprises a 47-mm Empore(TM) chelating disk as receiving phase and polyethersulfone as diffusion membrane. For monitoring organotins, the receiving phase is a 47-mm Empore(TM) C-18 disk, and the diffusion membrane is cellulose acetate. ICP-MS and GC-ICPMS/GC-FPD were used for inorganic mercury and the organotins analysis, respectively. The effects of environmental variables such as pH and salinity that could influence accumulation of test substances in receiving phase were studied. Linear uptake for all compounds was observed for at least 14 days of exposure at a constant aqueous analyte concentration in a flow-through system under controlled conditions of temperature, turbulence, and analyte concentration. Compound-specific sampling rates at 11 degrees C and simulated water turbulence of 40cms(-1) varied between 0.018 and 0.137Ld(-1). Compounds collected by the sampler exhibited detection limits ranging between 0.7 and 5.9ngL(-1). The feasibility of using these samplers in the field was tested in a polluted commercial harbour. The behaviour of the samplers to monitor target compounds was compared with those obtained from spot samples of water taken throughout the field deployment period. Data from laboratory studies and field trial support the feasibility of these samplers to measure the freely dissolved fraction of these important target analytes in water.