Beginning in September 1975, ozone replaced chlorine in a crossfire induced draft-cooling tower at a Henkel Corporation, Emery Group organic chemical manufacturing facility (Building 60) in Cincinnati. A year later a sister chemical plant (Building 68) in Cincinnati adopted ozone for its cooling tower. The results from these two applications were first reported in an address delivered to the International Ozone Association in June of 1981. This paper reviews the operation of these systems since the 1981 address. The two towers have continued to use ozone during the last ten years, in conjunction with a chromate corrosion inhibitor package. The chromate package was discontinued in early 1990 and a costs/benefits evaluation of ozone only treatment versus treatment with an organophosphate/zinc corrosion inhibitor package, with various biocides, has recently been performed. Building 60's tower has been treated with ozone only and building 68's tower with a Betz 35K program. The results of the two tower programs has been mixed. Continuation of the testing is being done to try to mix the benefits of both programs.