Nodulated Arachis hypogaea plants contain an allantoinase in the nodules that is different from the host tissue enzyme. The root and nodule allantoinases have been purified 10 and 15 fold respectively. They exhibited K m values of 25 (root) and 8.7 mM (nodule) for allantoin. Nodule allantoinase exhibits two pH optima, a major one at pH 6 and a minor one at pH 4 and is also specifically inhibited by parabanic acid and to a lesser extent by oxaluric acid. Arachis root tissue allantoinase, on the other hand, has a single pH optimum at pH 7.2 and is not inhibited by parabanic acid or oxaluric acid.