Biological H(2) production offers distinctive advantages for environmental protection over existing physico-chemical methods. This study focuses specifically on hydrogenases, a class of enzymes that serves to effectively catalyze H(2) formation from protons or oxidation to protons. It reviews the classification kschemes (i.e. [NiFe]-, [FeFe]-, and [Fe]-hydrogenases) and properties of these enzymes, which are essential to understand the mechanisms for H(2) production, the control of cell metabolism, and subsequent increases in H(2) production. There are five kinds of biological hydrogen production methods, categorized based upon the light energy requirement, and feedstock sources. The genetic engineering work on hydrogenase to enhance H(2) production is reviewed here. Further discussions in this study include nitrogenase, an enzyme that normally catalyzes the reduction of N(2) to ammonia but is also able to produce H(2) under photo-heterotrophic conditions, as well as other applicable fields of hydrogenase other than H(2) production. (C) 2011 Elsevier Ltd. All rights reserved.