Mechanisms of adherence to vascular endothelial cells by microorganisms on a molecular level can be elucidated by using monoclonal antibodies, purified cell wall constituents, and receptor analogues. Since these agents are expensive and available in limited quantities, a microsystem for probing adherence mechanisms to these cells has become essential. We studied techniques to accurately quantify the adherence of L-[35S]methionine-labeled Candida albicans to human umbilical vein endothelial cells in a 96-well microtiter plate system while avoiding specific problems related to Candida coadherence and avid binding to plastic. The endothelial cells were grown on a collagen matrix in individually detachable microwells enabling the determination of the number of adherent organisms from radioactive counts of the entire well. This procedure has the critically important advantage of obviating the need to remove adherent Candida from the wells. Expressing adherence to endothelial cell monolayers as the percentage of total organisms added to each well significantly decreases the variability of the assay.