Biotransformation of benzaldehyde to L-phenylacetylcarbinol (L-PAC) as a key intermediate for L-ephedrine synthesis has been evaluated using immobilized Cannida utilis. During biotransformation, the benzaldehyde level and respiratory quotient significantly affected both L-PAC and by-product benzyl alcohol formation. By controlling the benzaldehyde level at 2 g/l, maintaining a respiratory quotient of 5-7 and pulse feeding glucose, a final concentration of 15.2 g/l L-PAC was achieved in a fed-batch process. This compares with previous published results of 10-12 g/l in batch culture and 10 g/l L-PAC in a semicontinuous process with immobilized Saccharomyces cerevisiae. In a single stage continuous process with immobilized C. utilis, the steady state L-PAC concentration was significantly reduced because of the sustained toxic effects of benzaldehyde.