We have measured the change in the phase separation temperature, TC, in calf nuclear homogenate produced by a variety of naturally occurring cellular constituents. For all of the compounds studied, increasing concentrations of test compound were found to lower TC. Phosphorylated nucleotides had the greatest effect, lowering TCby 165–305μ/mole of test compound. Reduced and oxidized glutathione reduced TCby 69 and 100°C/mole, respectively. Smaller effects were observed for amino and ascorbic acids and sugars. The pH of the homogenate was also found to affect TCIn the normal lens, the concentration of each of these constitutents is small. Therefore, for each individual component, the cataract associated decrease in concentration is insufficient to produce the large increase in TCthat has been observed during cataractogenesis in some model systems. However, the superposition of the effects of changes in many cellular constituents (including pH and hydration) could possible produce a change in TCmore consistent with the experimentally observed one. In support of this, we have found that combinations of test compound have an additive effect on the TCof the nuclear homogenate.