Pseudomonas acidovorans lacks a number of enzymes of the salvage pathways of nucleic acid metabolism, including uridine phosphorylase, purine nucleoside phosphorylase, cytidine (deoxycytidine) deaminase and thymidine phosphorylase, and probably uridine kinase and deoxycytidine kinase. Its growth is inhibited by adenosine and deoxyadenosine. The level of aspartate transcarbamylase is the same in extracts of P. acidovorans grown in minimal medium ± 25 μg uracil/ml, and the enzyme appears to be insensitive to nucleotides which affect this enzyme in other bacteria. Growth of two pyrimidine-requiring mutants of P. acidovorans is supported by uracil or cytosine but not by their nucleosides nor by intermediates of the de novo pyrimidine biosynthetic pathway. Concentrations of uracil greater than 50 μg/ml have the unusual effect of lengthening the lag period of the mutants. The wild-type strain is not inhibited by uracil.