A procedure was developed for the simultaneous isolation of pure vicine [2,6-diamino-4,5-dihydroxypyrimidine 5-(β-D-glucopyranoside)] and convicine [2,4,5-trihydroxy-6-aminopyrimidine 5-(β-D-glucopyranoside)] from faba beans (Vicia faba L.). The procedure involves the extraction of the glycosides from faba bean protein concentrate by a neutral or basic acetone-water solution and concentration of the extract to a minimal volume, followed by lowering of the pH to neutrality when required. After standing approximately 3 days the vicine and convicine crystals are harvested and washed by centrifugation. Vicine can be readily obtained from the mixed crystals by extraction at a low pH since vicine is highly soluble while convicine is highly insoluble at this pH. Vicine can be recrystallized by adjustment of the pH of the acidic or basic solutions to neutrality. The relatively insoluble convicine is readily solubilized in a basic solution and can be recrystallized by lowering the pH to neutrality. Initial studies on the solubility and stability of vicine and convicine at different pH levels provided the basis for the development of the isolation procedure.