The nucleotide components of Polytoma uvella grown in shaken cultures have been examined, and fluctuations in their individual concentrations assessed during the three phases of growth. The most marked change in the nucleotide pool occurs between 30–58 h (end of lag and onset of log phase), when a relatively large increase was observed in the concentration of all the components; the most significant increases were in the nucleoside 5′-triphosphates, UDP-glucose, and ADP-glucose. Before the end of log phase the concentrations of CTP, ATP, GTP, and UTP had decreased whereas those of UDP-glucose and ADP-glucose did not do so until after the onset of the stationary period. At this time the concentration of pyridine nucleotide had increased. There was a predominance of purine nucleotides throughout the growth of the cultures and further, at all stages, a preponderance of adenine and uracil nucleotides existed over those of cytosine and guanine. By 144 h (late stationary phase) the concentration of each nucleotide had fallen considerably.