In some populations of the salamander Plethodon cinereus, two polymorphic esterase loci are in linkage disequilibrium. Short-term stability of the linkage disequilibrium is demonstrated by an age class analysis. Long, perhaps very long, term stability is suggested by its distribution. This stability and concordant geographic variation in allelic frequencies imply selective origin and maintenance. Data on the frequencies of two color morphs suggest that formation of the linkage disequilibrium is dependent on the genetic background.