The effects of parameters including water content, the amount of celite and the co-factor regeneration system on reduction of benzaldehyde to benzyl alcohol by yeast alcohol dehydrogenase (YADH) immobilized on celite in nonconventional media were investigated. Kinetic parameters (apparent) such as V-max, K-m, and k(cat) for different organic solvents used (butyl acetate, hexane, heptane and i-octane) were determined. K,values for benzaldehyde increased as the solvent was varied in the following manner : butyl acetate < hexane < i-octane < heptane. The highest k(m) value (20.26 mmol/L) was noted in heptane and the lowest (3.24 mmol/L) in butyl acetate. The V-max value in heptane was more than an order of magnitude higher than that in butyl acetate. Catalytic efficiencies (as expressed by k(cat)/K-m) ranged from 0.703 x 10(-4) L/mol . s for hexane to 0.171 x 10-4 L/mol . s for butyl acetate. In general, linear relationships were observed between k(cat)/K-m and the following solvent physico-chemical constants : dielectric constant, epsilon, logarithm of the saturated molar solubility of water in the organic solvents, log S-w/o, logarithm of partition coefficient of organic solvent in water/octanol two-phase system, log P, Hildebrand solubility parameter, delta, and solvatochromism of pyridinium-N-phenoxide betaine dye, ET(30).