Saccharomyces cerevisiae was immobilised in wet spun calcium alginate fibres for use in a bioreactor as an immobilised catalyst. The actual fibre production system was studied to determine optimum conditions when the fibre was used in the NADH reaction. The extrusion pressure and fibre winding speed were identified as the important variables and were optimised at 0.4 bar (g) and 300 rpm respectively. Other variables had little effect on the efficiency of the whole system.