Growth of the chemical industry since the end of World War II has been phenomenal, and one of the most striking advances has taken place in the synthetic detergent industry. The single largest volume product is prepared by sulfonating the petrochemical-based intermediate, dodecylbenzene. The economical, large-volume production of this intermediate suggests its utilization as an intermediate in the manufacture of additional chemicals. One promising possible use of dodecylbenzene is the preparation of quaternary ammonium compounds, which are surface and germicidally active, as well as algaecidal. The latter property of the quaternary ammonium compounds suggests their application as algaecides in fresh-water cooling systems where algae and slime accumulations are a problem of considerable magnitude. Field tests were conducted with the quaternary, N-dodecylbenzyl-N,N, N-trimethylammonium chloride, in two different types of industrial cooling water systems for a period of over 2 years. During this test period both systems were kept substantially free of algae and slime. These results introduce a new petrochemicals-derived product for maintaining algae and slime control in fresh water cooling systems at an economical cost level.