ABSTRACT. A diffusion enrichment technique is presented which allows for chemical enrichment of soft surficial and shallow subsurface sediments and subsequent measurement of O2 production. The sediment is enriched by inserting a perforated tube containing dialysis tubing filled with a nutrient/agar mixture. O2 production by surficial sediment is measured using an inverted, translucent, polyethylene chamber over the sediment. The inside of the chamber contains a collapsible bag connected to the water outside the chamber. When water overlying the sediment is withdrawn from a sampling port, it is displaced with water from outside the chamber, thus preventing contamination of water samples with pore water from below. The technique was tested be enriching near-shore sediments in a large oligotrophic lake with inorganic N and P. NH4(+) additions significantly stimulated benthic primary production as measured by O2 production, whereas enrichment with PO4(3-) had no effect.