A procedure is described for the dilution and storage of antisera in glass staining jars into which whole slides are immersed for incubation during light microscopic neuropeptide immunocytochemistry. Diluted antisera, stored at 4 degrees C and continuously reused, were found to be stable for long periods of time (to date over 3 years), and consistently yielded high quality staining in both single- and two-color immunoperoxidase staining. We found this procedure to be more convenient than conventional incubation procedures, allowing the more rapid processing of large numbers of slides and reducing the loss of slides due to technical errors. The consistency and reproducibility of day to day staining were also improved. The immersion of whole slides into the antisera permitted the use of long incubation times (up to 7 days) without the sections drying out, which in many cases substantially enhanced the sensitivity of the staining obtained. A procedure for two-color immunoperoxidase staining is described using diaminobenzidine for a brown color and alpha-naphthol/pyronin for a red/purple color. We found the alpha-naphthol/pyronin reaction superior to the more commonly used 4-chlornaphthol reaction as a second color. The two-color staining was found useful not only for demonstrating nerve cell bodies stained different colors, but also for staining nerve terminals one color that are around and contacting nerve cell bodies stained another color.