Culture supernatants of metabolically labeled Leishmania donovani promastigotes were shown to contain approximately 40 electrophoretically distinct released protein compounds. Of these, approximately 20 were glycoproteins which contained terminal mannose residues, as judged by their specific binding to concanavalin A-agarose beads. Smaller subsets of the released glycoproteins were bound by agarose-conjugated Lens culinaris, Ricinus communis, and peanut lectins. Promastigote mannose-containing released glycoproteins were isolated by concanavalin A affinity chromatography and used to immunize a rabbit. This antiserum recognized the parasite-released mannose-containing glycoproteins, including the soluble acid phosphatase, both by immunoprecipitation from solution and in immunoblot analyses. In an antibody bridged enzyme assay this polyspecific serum was also capable of binding native acid phosphatase out of solution and bridging it to the denatured enzyme on SDS-PAGE transblots. Although this antiserum was raised against all 20 released glycoproteins, in agarose gels its major precipitin activity was against the secreted soluble acid phosphatase.