Different aspects of biocatalysis are discussed with a view to obtaining products in a practical way using microorganisms and enzymes in catalytic amounts but as if they were organic reagents. A limited number of reactions catalysed by microbial reagents have been examinded according to the following classes: C-C bond formation, including the reaction catalyzed by aldolases, enantiomeric oxynitrilases, and decarboxylases. Oxidations promoted by microorganisms leading to Bayer-Williger-type products and hydroxylation at saturated carbon also includes the production of synthons derived from the microbial oxidation of substituted aromatics of wide synthetic applications. Reductions of carbonyl group with yeasts and other microorganisms, including the factor affecting the stereoselectivity when using all-cell organisms. Group transfer reactions describes synthetic achievements and theoretical aspects concerning the use of lipases, esterases and acylases. Industrial applications of microbial reagents in the large-scale production of fine chemicals offers validation to the basic research in the field.