The results of biochemical research are used extensively in the world outside the laboratory - in agriculture, medical sciences, nutrition, and many other fields. In clinical chemistry, biochemical measurements on people help diagnose illnesses and monitor responses to treatment. Liver disease is now routinely diagnosed and monitored by measurements of blood levels of enzymes called transaminases and of a hemoglobin breakdown product called bilirubin.

Pharmacology and toxicology are concerned with the effects of external chemical substances on metabolism. Drugs and poisons usually act by interfering with specific metabolic pathways. A good example is the antibiotic penicillin, which kills bacteria by inhibiting an enzyme that synthesizes an essential polysaccharide of the bacterial cell wall. Because animal cells do not synthesize these polysaccharides, they are not harmed by this inhibitor, which can therefore be used therapeutically.

A particularly exciting prospect in contemporary biochemistry is that of creating so-called designer drugs. If the target site for action of a drug is a protein enzyme or receptor, determining the detailed molecular structure of that target allows us to design inhibitors that bind to it with great selectivity. Early products of this drug architecture are now being tested. In the mid-1980s the detailed molecular structures of viruses began to be determined, opening the possibility of rational design of antiviral agents as well.

Herbicides and pesticides, in many instances, act in similar ways - by blocking enzymes or receptors in the target organism. The first generations of these toxic agents (such as DDT) were so nonspecific in their effects that organisms other than the target populations were often affected, resulting in unforeseen and often severe damage to the environment. Furthermore, the indiscriminate use of these agents gave rise to resistant target populations, so that an ever-increasing number of toxins needed to be used. Biochemistry is involved in understanding the actions of herbicides and pesticides, in increasing their selectivity, and in understanding and dealing with mechanisms by which target organisms become resistant to them. Thus, biochemistry has become an important component of environmental science.