Treatment of kainic acid with hydrochloric acid or bromine water yields kainlc acid lactone or bromokainic acid lactone but the same treatment of α-allokainic acid does not afford the lactone and non-lactonized hydroxy acid alone is obtained. These experimental results also suggest the appropriateness of determining the configuration of the carboxymethyl and isopropenyl groups in kainlc acid as in cis, and those in α-allokainic acid as in trans, which can rationally explain various reactions listed in Table I.