Sigma-Aldrich (NASDAQ: SIAL) provides a range of biochemicals and organic chemicals mostly in laboratory quantities.
Aldrich Chemical company is best known as a supplier of laboratory chemicals, especially organic chemicals. They are noted for excellent service and rapid delivery. Sigma chemicals also supplies laboratory chemicals, but the emphasis is biochemicals and supplies for clinical laboratories. Supelco is best known for its supplies used in the analysis of chemicals.
Aldrich is primarily a repackager and distributor of chemicals made by others, but also has facilities to manufacture and/or purify chemicals and does custom manufacturing. That includes manufacture of pharmaceutical intermediates.
Major competitors are Thermo Fisher Scientific, whose Fisher Scientific division supplies laboratory chemicals as well as lab equipment and Covidien, whose Mallinckrodt Baker division also makes and supplies laboratory chemicals.