Urease, in liquid and powder forms, with a purity meeting the requirements of diagnostic use, were partially purified from water melon Citrullus vulgaris cv. ＇Giza 1＇ seeds through a simple reproducible method consisting of delipidation, extraction, batch adsorption on TEAE-cellulose, filtration through Non Binding Protein Filter and lyophilization. The electrophoretic behaviour of the final preparation showed a single band for urease activity which coincided with the major protein band. To stabilize the solution form, 1 mM EDTA and 10% glycerol were routinely added to the enzyme solution during purification steps. To avoid contamination with microorganisms and maintain enzyme stability, 0.1% sodium azide and 0.01 mM dithiothreitol were added to the filtered enzyme, respectively. Urease in a powder form was prepared in absence of glycerol and lyophilized in presence of 2% dextran. The final preparation had a transparent appearance with free ammonia content less than 0.01 mu g unit(-1) and was stable for 14 months at 4 degrees C. Both liquid and powder ureases exhibited a distinct pH optimum at pH 8.0. Heat stability studies indicated that at pH 7.5 no loss of enzyme activities were recorded up to 40 degrees C for 30 min. The laboratory-prepared urea kits gave comparable activity to that of a commercially available bioMerieux urea kit for determining blood urea nitrogen (BUN).