Coronary endothelial cells not only produce vasoactive adenosine but also represent a metabolic barrier for this nucleoside. The purpose of the present experiments was to improve our understanding of the importance of the endothelial cells for the adjustment of the vascular adenosine concentration. Coronary endothelial cells of guinea pig heart grown to confluence on solid microcarrier beads were superfused in a chromatography column at 2 ml/min. Endothelial cell volume was determined with the 3-O-methyl-D-glucose method. Under control conditions the adenosine release in the coronary effluent perfusate averaged 0.6 pmol min-1 l-1. Measurement of the column adenosine release during infusion of specific inhibitors of the various pathways of adenosine metabolism and transport were used to assess intra- and extracellular adenosine production rates (4.5 vs. 1.1 pmol min-1 l-1). Assessment of the column outflow concentration during variation of the column inflow concentration permitted asses sment of the surface adenosine concentration of coronary endothelial cells which was found to range from 4 to 9 nM. These experimental data provide a basis for a model analysis in order to quantify the contribution of adenosine metabolism and transport of coronary endothelial cells to global cardiac adenosine production and to assess its influence on the capillary and interstitial adenosine concentration on the example of the guinea pig heart.