A high-cell-density fermentation process for production of an extracellular alginate lyase from Klebsiella pneumoniae on a defined medium has been developed. The process employs a strategy using two carbon sources, One low-molecular-mass, low-viscosity carbon source (sucrose) with high water solubility is used as the main carbon source for growth, while the high-molecular-mass and viscous alginate in low concentration is used as an inducer for enzyme synthesis. The repression of alginate lyase production by sucrose and the growth inhibition that we observed at increased levels of ammonia were circumvented by a computer-assisted fed-batch addition of the carbon sources (sucrose and alginate) and by supplying nitrogen sources as ammonia in the pH control. No enzyme production was observed when dissolved oxygen limited growth at an oxygen uptake rate of 40%-50% of the maximum uptake rate. An optimal composition of the feeding solution (12.5 g alginate and 587.5 g sucrose l(-1)) was found both for the maximum final concentration of enzyme (1330 Ul(-1)) and for the maximum volumetric rate of enzyme production (67 Ul(-1) h(-1)). The enzyme production depends on the growth rate in the linear growth phase, giving a maximum enzyme concentration at the highest growth rate tested. The final enzyme concentration shows a fivefold increase compared with previously reported data where alginate was used as a sole carbon source. In addition, the ratio of alginate lyase produced to alginate substrate consumed increased by a factor of approximately 15. A doubling in extracellular specific activity of the enzyme was observed, a property of significant interest, especially for purifiction of the enzyme. On the other hand, the final dry cell weight concentration of the bacteria also increased by a factor of 15-20 thus giving a relatively lower specific productivity of 0.4 U (g cell dry weight)(-1) h(-1).