The composition of gellan gum elaborated by wild type Sphingomonas paucimobilis was studied. Gas chromatographic methods of analysis were compared. Analysis of neutral sugars was carried out by Saemen hydrolysis and Stones method. Stones method was preferred due to its simplicity and the production of comparable results to those obtained following Saemen hydrolysis. The neutral sugars of gellan gum were analysed by GC/MS following preparation of per-methylated alditol acetates (PMAAs). Two methods were used for making alditol acetates, the Hakamori and sodium hydroxide (NaOH) methods. Although the NaOH method was simpler and faster to carry out, the results were not representative of the true composition of gellan gum. The Hakamori method revealed the presence of 33%, 1,4 rha, 30% 1,3 glc and 31% 1,4 glc in agreement with the sugar compositions of O'Neill et al. (1983) and Jansson et al. (1983) who elucidated the structure of gellan gum simultaneously. To determine the glucuronic acid content of gellan gum, samples were carboxy-reduced prior to analysis. Two methods were compared, the lithium aluminium deuteride and tetrahydrofuran (THF) methods. The THF method revealed the presence of 24%, 1, 4 rha, 24% 1,3 glc 26% 1,4 glc and 25% 1,4, 6 glc (corresponding to glcA). Physiological studies were carried out with twenty mutant strains of S. paucimobilis in batch culture. The chemical composition, viscosity, gelation and rheological properties of EPS produced from many of these strains were further investigated. Some of the strains elaborated polysaccharide, named fine precipitate, which differed chemically from gellan gum. Rheological measurements were carried out on several EPS samples using a mechanical rheometer. Large differences in gel strength were detected.