The bacteria were grown on the GYS medium in a 2-liter scale fermentor in batch mode operation under pH and temperature controlled conditions. Under this conditions the cell yield was doubled (9.5 mg/ml vs. 4.8 mg/ml dry cell weight) and the cultivation time was reduced to one third (60 vs. 180 hours) as compared with shaken flasks. These results are in good agreement with the literature [12]. We found that addition of 2 g/l cholesterol to the culture broth [12], prepared as an aqueous emulsion with the aid of Tween 80 at a weight ratio 2:1 results in a high yield of COX production [9], but the preparation procedure of that emulsion had a marked influence in the final enzyme yield, although not on the cell weight, as seen in Table 1. The spray-dry method resulted advantageous because the cholesterol :Tween 80 emulsion formed readily and COX production increased in overall by three times with respect to the preparation of the cholesterol:Tween 80 mixture at the flame. Enzyme production improvement resulted larger as cell-linked (3.8-fold) than as extracellular (2.3-fold). This overall increase of COX production can be due to a better availability of cholesterol to the cell since particle size obtained by spray-dry is smaller.