Under conventional cultural practices for burley tobacco, the pattern of soluble protein accumulation, namely Fraction I protein (F I protein) and Fraction II protein (F II protein), in bright (NC 95) and burley (Ky 14) tobaccos was similar during the growth seasons of 1977 and 1978. Their quantities reached maximal levels around flowering, followed by a gradual decline. However, the loss of F I protein was much more rapid than that of F II protein during leaf maturation. The two-year results revealed that Ky 14 contains significantly more F I protein, insoluble proteins, total proteins, free amino acids, total nitrogen, nitrate nitrogen, and total alkaloids than NC 95, if averaged over the growing season. The latter showed a greater amount of chlorophyll only. There was no difference in F II protein concentration between the two cultivars. On the basis of soluble protein concentration in leaf lamina and a double or quadruple plant population as plant size permits, the estimated yields of soluble proteins in Ky 14 at the immature plant stage, about one week before topping, and by harvest time are 888, 470 and 281 kg/ha, respectively. When including both soluble and insoluble proteins, the immature plants of NC 95 could yield 1,387 kg/ha of protein in comparison to 1,308 kg/ha for Ky 14. Multiple harvests of regrowth can further the protein yield per hectare. The present results strongly suggest that tobacco is a potential protein crop for the future.