Ureases (EC 3.5.1.5) are metalloenzymes that hydrolyse urea to produce ammonia and carbon dioxide. These enzymes are found in fungi, bacteria, plants, and show very similar structures. In bacteria, ureases are involved in the turnover of nitrogen compounds and pathogenesis of different clinical conditions caused by infection due to, for example, Proteus mirabilis or Helicobacter pylori. In spite of abundance of urease in vegetal tissues, mainly in leguminous seeds, the physiological role of this enzyme in plants is still poorly understood. Jack bean Canavalia ensiformis and soybean Glycine max have at least two isoforms of urease. It has been demonstrated that both isoforms of urease of Canavalia ensiformis and the embryo-specific urease of soybean have insecticidal activity. The cotton stainer bug Dysdercus peruvianus (Hemiptera) is highly susceptible (0.001%w/w) to the entomotoxic effect of these proteins. Since it is known that not all ureases have insecticidal activity for instance the Bacillus pasteurii urease is not toxic to the cotton stainer bug, and considering the wide distribution of ureases in plants, we decided to investigate the presence of urease in cotton Gossypium hirsutum seeds. Crude extracts of cotton seed showed urease activity of 1.5 mU per A280, corresponding to about 1/1000 of the urease activity of jackbean extracts. The ureolytic activity was precipitated in the 0.30-0.80 ammonium sulfate fraction, and after dialysis, this material was submitted to a chromatography in DEAE- cellulose, equilibrated in 20 mM NaPB, 5mM b-mercaptoethanol, 1mM EDTA, pH 7.5. Elution with 300 mM NaCl yielded an urease-enriched fraction. The kinetic parameters of this partially purified urease were very similar (Km for urea 1-8 mM, optimum pH 7.0) to other well known urease from leguminous and curcubitaceus plants. The enzymatic activity of the Gossypium hirsutum urease was reduced by acetohydroxamic acid and p-hydroximecuribenzoate in uM concentrations. To our knowledge, this is the first description of urease in Malvaceae. Supported by:  CAPES, FAPERGS, CNPq, FINEP.