Rp1 is a complex resistance locus of maize. Different Rp1 genes confer resistance to different common rust isolates and vary in their meiotic stability. Susceptible derivatives from Rp1 heterozygotes, and those with the combined resistance of both parents, are commonly associated with a single nonparental combination of flanking markers-indicating they arise by simple crossing-over, and that one of the penes maps distally or proximally to the other. Susceptible derivatives fram lines homozygous for unstable Rp1 genes exhibit both nonparental combinations of flanking markers-indicating they arise by unequal crossing-over. We analyzed derivatives from 10 different test cross populations to determine if such complex types of recombination events can occur in heterozygotes. The Rp1 penes used to construct the heterozygotes were known to vary in their meiotic stability. Recombinants with both nonparental combinations of flanking markers were found from three of the heterozygotes. All three hybrids carried at least one unstable gene. The occurrence of these recombinants indicates Rp1 genes reside on duplicated sequences which, in at least some lines, can mispair during meiosis. Implications for allelism tests for resistance penes, for the generation of a Rp1 area genetic fine structure map, and for transposon tagging strategies are discussed.