The co-occurrence in nature of normal- and ent-labdanes is surveyed, and the possibility is explored that the enzyme responsible for the cyclization of geranyl geraniol pyrophosphate to the labdane skeleton allows enantiomeric leakage to yield optically impure products. Naturally occurring manool and abienol have been isolated without enantiomeric fractionation and examined to evaluate in vivo optical purity.