AbstractThe characteristics of silver enhancement of immunogold staining at the electron microscopy level were evaluated. Five differently sized gold particles (1,5,15,30 and 40 nm) were tested for 10 different enhancement durations (1–17 min) with atrial natriuretic peptide in rat atria as a model. We found that the size of the particles grew in an accelerated fashion within certain time intervals. Beyond this duration, the variation in particle sizes and shapes increased out ofthe range ofany practical value. A semiquantitative correlation between particle size and the duration of silver treatment was derived. The silver enhancement did not affect the background of the immunostaining, and the silver enhanced 1 nm gold was not as sensitive as the 5 nm gold. An attempt was made to use these properties of silver enhancement in a double immunostaining procedure and we found that its application in this regard was feasible but limited. This study provides a quantitative basis for immunogold silver immunocytochemistry and can be used as a guideline for future applications. (The J Histotechnol16:19, 1993)