The level and balance of chemical constituents in flue-cured tobacco are determined by factors such as soil fertility, climatic conditions, cultivation practices and cultivars. The sugar-nicotine ratio in flue-cured leaves can be correlated to quality and it is therefore, necessary to perform optimum fertilization and topping practices and to identify certain cultivars. The effects of cultivation practices on the nicotine content, sugar content and marketable yield were evaluated for eight successive seasons, starting in 1992. Flue-cured entries, OD234, OD 469, OD 272, OD 242, TL 33, OD 2 and OD 1, were evaluated. Entries were tested on different soil types, from sandy soils with 4 % clay to clay loam soils with 33 to 36 % clay. During the first two growing seasons, the effects of topping height and different nitrogen fertilization levels were also evaluated. Nicotine content decreased with a higher topping depth, whereas marketable yield increased. Sugar content decreased with increased nitrogen levels ranging from 100 to 180 kg.ha^-1. During 1994 and 1995, the effect of four different nitrogen levels ranging from 100 to 160 kg.ha^-1 was evaluated. Nicotine content increased with increased nitrogen fertilization whereas sugar content decreased. If the nitrogenous constituents are high the sugar constituents are low. Marketable yield decreased with increased nitrogen fertilization. During 1996, 1997 and 1998, the lowest nicotine content was obtained at the lowest nitrogen level and the highest nicotine content at a nitrogen fertilization level of 190 kg.ha^-1. During 1999 and 2000 the nicotine content increased whereas the sugar content decreased with increased nitrogen levels ranging from 130 to 210 kg.ha^-1. However, within limits, the sugar-nicotine ratio of the tobacco leaf can be altered by changing the growing conditions, but a new set of cultivation practices will have to be evaluated to obtain high yields and good-quality leaves.