In 1980 Sr. sold his farm on contract to Ds. D made the installment payments until 1985. In 1985, Ds assigned the contract to Forrest Hatfield. Sometime prior to February 1986, Hatfield informed Ds he could no longer make the payments and returned the farm to them. D then met with Sr. to inform him they were also unable to make the upcoming March 1, 1986 payment. After negotiations, Sr. and Ds agreed to reduce the contract price along with some other changes from the original contract terms. Both parties signed an agreement dated March 7, 1986, created by Sr.'s attorney which reduced their negotiations to writing. Sr.'s attorney later recorded the agreement. Ds made all payments due under the 1986 agreement. Sr. has resided in a nursing home since 1985. In 1988 Sr. established a voluntary conservatorship appointing his two children, Ps co-conservators for himself. Ps filed this lawsuit on September 12, 1988, seeking a declaratory judgment that Ds were in default of the 1980 contract. Ps alleged the 1986 agreement was unenforceable due to lack of consideration. The district court overruled Ps' motion for partial summary judgment finding lack of consideration was not a triable issue because Ps failed to specially plead it as an affirmative defense. The jury found Sr. was mentally competent when he entered into the 1986 agreement. The court then held a bench trial on the equitable issues of fraud and undue influence. The court entered a verdict in favor of the Ds, finding the 1986 agreement enforceable. Ps appealed. They contend the issue of lack of consideration should have been submitted to the jury because a reply pleading was unnecessary.