Amygdalin, often referred to as B17, is a naturally occurring molecule found in over 1,200 different foods including fruits, vegetables, nuts, grains, and seeds. Vitamin B17 is found in concentrated amounts in the seeds of apricots, plums, cherries, oranges, nectarines, apples, peaches, and many other fruits. Amygdalin is a powerful phytonutrient that is found in apricot kernels and is found in the highest concentrations and with the most effective accompanying enzymes in apricot seed kernels.
From CancerTutor.com/laetrile: Laetrile is believed to fight cancer by targeting and killing cancer cells and building the immune system to help fend off future outbreaks of cancer. It actually uses two different methods to accomplish these goals. The first method revolves around enzymes. Vitamin B-17 is made up of glucose plus two potentially toxic substances — benzaldehyde and hydrogen cyanide. (Note: In the early days of laetrile research it was assumed that cyanide was the major cancer cell-killing molecule, but now many researchers believe benzaldehyde is the primary reason the cancer cell is killed.) Healthy cells contain the enzyme rhodanese (in his book World Without Cancer, G. Edward Griffin calls this the protecting enzyme). Rhodanese protects the cells by neutralizing the benzaldehyde and cyanide in B-17, converting them to useful compounds, including thiocyanate, which is known as a natural regulator of blood pressure and also is involved with the production of Vitamin B-12. However, cancer cells do not have rhodanese. Instead, they have an enzyme called beta-glucosidase (Griffin calls this the unlocking enzyme). Beta-glucosidase unlocks the benzaldehyde and cyanide from the glucose to create a targeted poison that kills the cancer cell.