The effects of extended anaerobic treatments on Vicia faba lateral root-tip chromosomes were determined. It was observed that aberrations resulted from these treatments, and that the frequency varied from root to root as well as from experiment to experiment. It was suggested that the inconsistency observed might be due to variation in the abilities of different roots to produce energy via fermentation routes. If this were true, an inhibition of fermentation would result in a more consistent aberration frequency. A fermentation inhibitor, NaF, was used in combination with extended anaerobic treatments. The observed frequency of aberrations after the combined treatments was generally higher and considerably less variable. Although other hypotheses might account for the NaF effect, the hypothesis most compatible with the evidence is that the effect is due to energy deprivation. The experimental results are discussed in terms of the aforementioned effect and in terms of three alternative hypotheses for the production of chromosomal aberrations as a consequence of a lack of energy. It is concluded that damage might result from a build-up of normal cellular compounds to abnormally high concentrations which would act directly or indirectly on the chromosomes, from the breakdown of DNA as an energy source, or simply as a result of the fact that the chromosome needs energy to remain intact.