A component of the Papain Dissociation System, for use in the tissue dissociation method of Huettner, J.E., and Baughman, R.W.: J. Neuroscience, 6, 3044 (1986). Contains papain, L-cysteine, and EDTA. This material is 0.22 micron membrane filtered and lyophilized in autoclaved vials. A vial reconstituted with 5 ml of EBSS or equivalent yields a solution at 20 units of papain per ml in 1mM L-cysteine with 0.5mM EDTA.