The intracellular distribution of multimerin in endothelial cells, evaluated by indirect immunolabeling and epifluorescent microscopy. Fixed, permeabilized endothelial cells were labeled with monoclonal and polyclonal antimultimerin, normal mouse IgG, or polyclonal antimultimerin preadsorbed with purified multimerin or with buffer (N indicates cell nuclei). The granular staining was similar in cells cultured for 24 hours with (c) or without (b) the protein synthesis inhibitor cycloheximide. Most of the multimerin-labeled granules were round to slightly elongated (b, c, d), but rod-shaped granules were also seen in some cells (a, h, i). The same cytoplasmic structures in endothelial cells were recognized by monoclonal and polyclonal antimultimerin (h and i show identical fields of a double-labeled cell). No fluorochrome was detected in the opposite channel of single labeled cells (d and e are paired images; same magnification, all panels).