The fluorescent pseudomonads Pseudomonas aeruginosa, Pseudomonas aureofaciens and Pseudomonas putida were examined for their ability to utilize pyrimidines and pyrimidine analogues. Both P. aeruginosa and P. aureofaciens grew upon dihydrouracil, dihydrothymine, uridine and cytidine as either a sole nitrogen or carbon source while uracil, thymine and cytosine served only as sole nitrogen sources for both pseudomonads. The only difference between the observed growth of P. aeruginosa and P. aureofaciens on pyrimidines was that deoxycytidine sustained the growth of P. aeruginosa as a nitrogen source. With respect to P. putida, uracil, cytosine and cytidine were found to be nitrogen sources while dihydrothymine, uridine and cytidine served as carbon sources. The fluorescent pseudomonads investigated had fourteen nutritional characteristics which were determined in common for the pyrimidines screened. All the fluorescent pseudomonads were sensitive to a low concentration of 5-fluorouracil. Inhibition by 5-fluorouridine of P. aureofaciens growth was observed at a low concentration while a high concentration of this analogue was required to halt P. putida growth. Neither P. aureofaciens nor P. putida could grow in the presence of a high concentration of 5-fluorocytosine. Only P. aureofaciens growth was noted to be inhibited by a high concentration of 6-azauracil.