Reports on the testing of ten cooling towers to determine possible correlations between Legionella numbers and physical, chemical, biological and operational parameters. States significant correlations were found between total bacteria and Legionella levels as measured by direct fluorescent antibody techniques. Notes that five biocides were tested for efficacy in controlling Legionella and other microbial populations in four towers. The results showed that most biocides were ineffective at manufacturers' suggested dosages. Only frequent, high doses of organic biocides or low-level continuous treatment with an oxidising biocide showed promise for long-term control of microorganisms in the towers tested.

KEYWORDS: Testing, cooling towers, USA, bacteria, Legionnaires disease, biocides