In this study , the nature of variability observed in previous experiments, when leaf explants of sugar beet (Beta vulgaris L.) were cultured in vitro, was investigated at different levels of classification (i.e., variety, plant and organ). Large differences in rooting capacity were observed when 10 commercial varieties were compared. Significant inter-plant and inter-leaf (intra-plant) variability was found to exist within a variety but explants taken from different positions within the leaf behaved similarly. A two-fold variation in polyphenol-oxidase activity was found within a population of the variety Primo, but no relationship existed between enzyme activity and either root formation or the blackening of the explant tissue when compared by culturing explants taken from the same leaves used for enzyme assays, although a weak negative correlation between the degree of blackening and rooting capacity was observed.