Concentrations of bacteria, cadmium, and lead found in particulates taken from a San Francisco Bay salt marsh were determined. Data indicate that the salt marsh microlayer contains high concentrations of particulates, microorganisms, and lead; the presence of lead and bacteria on particulate surfaces indicates that microlayer particulate surfaces may be a major source of lead uptake in estuarine ecosystems. (3 graphs, 3 photos, 23 references, 2 tables)