The three genotypes, Su/Su, Su/su, su/su, of John Williams Broadleaf tobacco (Nicotiana tabacum) grew equally well on Murashige-Skoog medium. On a fresh weight basis, the heterozygous (Su/su) yellow mutant and the homozygous (su/su) wild type plants contain similar amounts of RuBPCase (Fraction I Protein) and Fraction II Protein in roughly equal proportions, but with a somewhat reduced amount of 70S and 80S free ribosomes. The homozygous albino (Su/Su) plants contain appreciable amounts of RuBPCase and free 70S ribosomes, although the chlorophyll levels are extremely low. In the case of the yellow and albino forms, there appears to be no correlation between RuBPCase and chlorophyll content. When equal concentrations (1 mg/l) of kinetin and indole-3-acetic acid (IAA), or kinetin alone, were added to the medium, a drastic reduction of RuBPCase and disappearance of free 70S ribosomes were observed in the yellow mutant and wild type plants, whereas the effect on the albino plants was not significant.