ALK or Alk may refer to:
In organic chemistry, an alkane, or paraffin (a historical name that also has other meanings), is an acyclic saturated hydrocarbon.
The alkaline earth metals are six chemical elements in column (group) 2 of the Periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
In organic chemistry, an alkene is an unsaturated hydrocarbon that contains at least one carbon–carbon double bond.
Alkaloids are a group of naturally occurring chemical compounds that mostly contain basic nitrogen atoms.
Alkaline phosphatase (ALP, ALKP, ALPase, Alk Phos) (EC 22.214.171.124) is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids.