Cytochromes are coloured iron-containing proteins that transfer electrons during cellular respiration and photosynthesis. The Cytochrome P450 family of enzymes catalyze reactions whereby water-insoluble drugs or metabolites, that would otherwise reach toxic levels in cell membranes, are rendered suitably water-soluble to leave the cell and be excreted in the urine. This reference reviews the current status of the P450 field in terms of our present knowledge and understanding of the enzymes' structure and function, including their multiplicity of forms, diversity of substrates and selectivity....