The kinetics of growth and xanthan production by X. campestris ATCC 1395 in batch culture were studied in laboratory fermenter without pH control. Fermentations were carried out over a range of stirrer speeds from 100 to 600 rpm, which covered the entire range of stirrer speeds practical for the bioreactor used. Fig. 1 shows the time-courses of two fermentations carried out at 100 and 600 rpm. Cell dry-weight, xanthan and residual glucose concentrations, as well as the culture pH, are presented over a time course of 72 h. Increased agitation levels resulted in higher production levels — xanthan production almost doubled as the stirrer speed increased from 100 to 600 rpm and similar was the effect on cell growth.