Sucrose to ethanol conversion by Zymomonas mobilis is investigated. The fermentation pattern of sucrose to ethanol conversion was established using two strains of Z. mobilis derived from NCIB 11199 (Z7) and NCIB 8939 (Z10). The use of pH control at 4.5 and above by sodium hydroxide addition and an increase in incubation temperature from 30 to 35° C reduced fermentation times from 50 h to 25 h. The addition of peptone to the culture medium at 2.0 g.l-1 concentration, in the presence of 2.0 g.l01 each of yeast extract, KH2PO4, MgSO4.7H2O and (NH4)2SO4, improved ethanol yields from 70 to 75%, to 80 to 85% with 200 g.l-1 sucrose as the energy source.Zymomonas mobilis strain Z7 showed an increase with respect to the specific growth rate, the velocity of sucrose hydrolysis, glucose uptake and ethanol productivity rate in the sucrose concentration range 20 to 100 g.l-1 with no significant trend evident in the range 100 to 200 g.l-1 sucrose.Levan sucrase purified from Z. mobilis strain Z7 was inhibited competitively by glucose (Ki = 5.3 x 10-3 M = 0.96 g.l-1) and noncompetitively by ethanol (Ki = 8.4 x 10-1 M = 33.7 g.l-1). Levan sucrase purified from cell free extracts and culture supernatants showed no detectable differences and were regarded as the same enzyme species.The fermentation pattern of sucrose to ethanol conversion by Z. mobilis may be resolved into four stages (1) An initial stage of free glucose (and fructose) utilization associated with biomass formation, (2) The sucrose hydrolysis phase which occurs when initial free glucose has declined to less than 1 g.l-1, (3) Biomass formation continues as glucose and fructose released from sucrose is utilized, (4) Glucose and fructose are exhausted and ethanol (and carbon dioxide) production reaches a maximum with 15 to 20 g.l-1 sucrose remaining unutilized from an initial sucrose concentration of 200 g.l-1.The inhibition of levan sucrase by glucose and ethanol explain aspects of the sucrose to ethanol fermentation pattern. Sucrose is not completely utilized once hydrolysis has commenced, because accumulated glucose inhibits levan sucrase activity toward sucrose. When glucose (and fructose) have been exhausted, the accumulated ethanol inhibits further sucrose hydrolysis.Once induced, levan sucrase synthesis and release continues, as it is demonstrated that in continuous cultures on 200 g.l-1 sucrose sucrose hydrolyzing activity persists in the presence of glucose (up to 35 g.l-1) and ethanol (79 g.l-1).Zymomonas mobilis is able to meet its nutritional requirements when grown on several commercially available sources of sugar cane juice. Supplementation with yeast extract, pantothenic acid or peptone was not required. Ethanol yields obtained were as high as those obtained using semi-defined medium.The viability of sucrose to ethanol conversion by Z. mobilis has been demonstrated and further investigation and a comprehensive economic evaluation is now warranted.