It was our goal to determine the location of the intermediate chain within the complex of cytoplasmic dynein by immunoelectron microscopy. To do so we generated two monoclonal antibodies (m74-1 and m74-2) specific for the intermediate chain, Both antibodies recognised the intermediate chain by sodium dodecyl sulphate-polyacrylamide gel electrophoresis immunoblot and ELISA assays of native and denatured proteins. When sucrose density gradient-purified cytoplasmic dynein from bovine brain was incubated with the gold-conjugated monoclonal antibodies, m74-1 and m74-2, and examined by negative staining, the gold label was found opposite the globular heads at the base of the V-shaped stalk of the motor complex, The labelling of the intermediate chain is the first mapping of a component within cytoplasmic dynein, The identification of the intermediate chain at the base of the complex supports a possible docking function of the intermediate chain. (C) 1996 Academic Press