Studies on the nutritional requirements for optimal exopolysaccharide (EPS) production by Sphingomonas paucimobilis-GS1, in a synthetic medium revealed sucrose (40 g/L) and glutamate (0.5 g/L) or KNO3 (1 g/L) to be the most suitable carbon and nitrogen sources, respectively. Ammonium salts were unfavorable to EPS accumulation, and inorganic phosphate above 10 mM affected the polymer quality. Specific activities of the EPS precursor-forming enzymes, UDP glucose pyrophosphorylase (UDPGPP) and phosphoglucomutase (PGluM), were four to five times lower, whereas that of UDPglucose dehydrogenase (UDPGDH) was 15-20 times lower under media conditions not favoring EPS production than under conditions favoring EPS accumulation. The activity of hexokinase (HK), however, remained constant. Considerably lower specific activities of PGluM and UDPGPP were also detected in some of the non-mucoid mutants.